user7141: What are the proper relax / Sleep practices for a practitioner of meditation methods?
As to Buddhist point of view what is sleep and how to cope with it?

user-1: As Suminda wrote in his answer, eleven benefits of freedom of mind through metta are listed by the Buddha, among them:

"One sleeps easily, wakes easily, dreams no evil dreams."
  --AN 11.16

More generally, the Buddha has said he sleeps at ease even in unpleasant circumstances because he abandoned craving, aversion and delusion (AN 3.34).
He also said about monks in training:

"These three things lead to the falling away of a monk in training. Which three? There is the case where a monk in training enjoys activity, delights in activity, is intent on his enjoyment of activity. He enjoys chatter, delights in chatter, is intent on his enjoyment of chatter. He enjoys sleep, delights in sleep, is intent on his enjoyment of sleep. These are the three things that lead to the falling away of a monk in training.
"These three things lead to the non-falling away of a monk in training. Which three? There is the case where a monk in training doesn't enjoy activity, doesn't delight in activity, isn't intent on his enjoyment of activity. He doesn't enjoy chatter, doesn't delight in chatter, isn't intent on his enjoyment of chatter. He doesn't enjoy sleep, doesn't delight in sleep, isn't intent on his enjoyment of sleep. These are the three things that lead to the non-falling away of a monk in training."
-- Iti 3.30

In AN 7.58 the Buddha instructs Ven. Maha Moggallana on how to overcome his drowsiness:

"Well then, Moggallana, whatever perception you have in mind when drowsiness descends on you, don't attend to that perception, don't pursue it. It's possible that by doing this you will shake off your drowsiness.
"But if by doing this you don't shake off your drowsiness, then recall to your awareness the Dhamma as you have heard & memorized it, re-examine it & ponder it over in your mind. It's possible that by doing this you will shake off your drowsiness.
"But if by doing this you don't shake off your drowsiness, then repeat aloud in detail the Dhamma as you have heard & memorized it. It's possible that by doing this you will shake off your drowsiness.
"But if by doing this you don't shake off your drowsiness, then pull both your earlobes and rub your limbs with your hands. It's possible that by doing this you will shake off your drowsiness.
"But if by doing this you don't shake off your drowsiness, then get up from your seat and, after washing your eyes out with water, look around in all directions and upward to the major stars & constellations. It's possible that by doing this you will shake off your drowsiness.
"But if by doing this you don't shake off your drowsiness, then attend to the perception of light, resolve on the perception of daytime, [dwelling] by night as by day, and by day as by night. By means of an awareness thus open & unhampered, develop a brightened mind. It's possible that by doing this you will shake off your drowsiness.
"But if by doing this you don't shake off your drowsiness, then — percipient of what lies in front & behind — set a distance to meditate walking back & forth, your senses inwardly immersed, your mind not straying outwards. It's possible that by doing this you will shake off your drowsiness.
"But if by doing this you don't shake off your drowsiness, then — reclining on your right side — take up the lion's posture, one foot placed on top of the other, mindful, alert, with your mind set on getting up. As soon as you wake up, get up quickly, with the thought, 'I won't stay indulging in the pleasure of lying down, the pleasure of reclining, the pleasure of drowsiness.' That is how you should train yourself.

His last advice above is a general instruction on how to sleep and how the Buddha himself is described sleeping. He also describes elsewhere (AN 4.37) how a monk is "devoted to wakefulness":

"And how is a monk devoted to wakefulness? There is the case where a monk during the day, sitting & pacing back & forth, cleanses his mind of any qualities that would hold the mind in check. During the first watch of the night, sitting & pacing back & forth, he cleanses his mind of any qualities that would hold the mind in check. During the second watch of the night, reclining on his right side, he takes up the lion's posture, one foot placed on top of the other, mindful, alert, with his mind set on getting up [either as soon as he awakens or at a particular time]. During the last watch of the night, sitting & pacing back & forth, he cleanses his mind of any qualities that would hold the mind in check. This is how a monk is devoted to wakefulness.


user631: Monks, eleven advantages are to be expected from the release (deliverance) of heart by familiarizing oneself with thoughts of loving-kindness (metta), by the cultivation of loving-kindness, by constantly increasing these thoughts, by regarding loving-kindness as a vehicle (of expression), and also as something to be treasured, by living in conformity with these thoughts, by putting these ideas into practice, and by establishing them. What are the eleven?

"He sleeps in comfort. 2. He awakes in comfort. 3. He sees no evil dreams. 4. He is dear to human beings. 5. He is dear to non-human beings. 6. Devas (gods) protect him. 7. Fire, poison, and sword cannot touch him. 8. His mind can concentrate quickly. 9. His countenance is serene. 10. He dies without being confused in mind. 11. If he fails to attain arahantship (the highest sanctity) here and now, he will be reborn in the brahma-world.

(Mettanisamsa Sutta)

user295: 
What are the proper relax / Sleep practices for a practitioner of meditation methods?

If you do Metta meditation before sleeping you are better off, as one benefit of Metta is you sleep well. ((Aṭṭha) Mettânisansa Sutta, (Ekā,dasa) Mettânisansa Sutta)

As to Buddhist point of view what is sleep and how to cope with it?

This is when your Bhavanga is active and the revolutions of the Dependent Origination cycles has momentarily stopped. (The Doctrine of Paticcasamuppada - The Law Of Independent Origination - By U Than Daing, page 32). An essay "The Unconscious" by Piya Tan discusses action action that done when sleeping.
--
Thoughts of others on the subject of sleep:
On deep sleep and bhavanga:

The idea of an underlying skilful base to the mind is developed further in the
  Abhidhamma, which analyses the constituents of consciousness in detail. For a
  human rebirth to have occurred, the bhavakga, or consciousness to which the
  mind returns at rest, is skilful, whether with the two roots of non-greed and nonhatred,
  or more usually, with three roots, of wisdom, non-greed and non-hatred.
  This consciousness will be present whenever the mind enters bhavakga, either
  momentarily at the end of each thought-process, or during deep sleep. For all born
  as humans, the state of bhavakga is a reflection of the skilful state of mind that
  must have been present at the moment of death as a governing factor for the
  relinking consciousness. It is passive, however, and this predisposition needs
  active cultivation during waking life. Only when skilful consciousness is present
  during daily life, or during meditation, does the mind become actively bright and
  radiant. According to the theory this happens, for instance, at the moment of
  giving, of being alert and interested or when practising jhana: the active part of
  the thought-process ( javana) is then free from defilements. Those practising
  meditation are ‘bringing into being’ a consciousness which is thought to be a kind
  of birthright, but which needs cultivation. In Buddhist countries the human realm
  is considered particularly important for spiritual work. Birth in heaven realms is
  pleasant but lacks the suffering to encourage spiritual work; the realms of
  animals, ghosts and hell beings are considered far too painful for the path, and it
  is difficult, though not impossible, for such beings to find a skilful rebirth. It is
  said that the Buddha always has a human birth as his last existence after many
  lifetimes spent preparing to teach others. One sutta compares rebirth in a hell
  realm as entering into a pit of coals, that of a heaven realm to a stay in a luxurious
  mansion. The human realm, however, is like a man sitting in the shade of a
  tree in a hot climate, also the classic conditions for the practice of meditation
  (see M I 76–7).

Source: Buddhist Meditation: An anthology from the Pali canon, by Sarah Shaw
On reduced need of sleep for meditations

Similarly, when you go to bed at night, close your eyes and feel sensation anywhere within the body. If you fall asleep with this awareness, naturally as soon as you wake up in the morning, you will be aware of sensation. Perhaps you may not sleep soundly, or you may even remain fully awake throughout the night. This is wonderful, provided you stay lying in bed and maintain awareness and equanimity. The body will receive the rest it needs, and there is no greater rest for the mind than to remain aware and equanimous. However, if you start worrying that you are developing insomnia, then you will generate tensions, and will feel exhausted the next day. Nor should you forcefully try to stay awake, remaining in a seated posture all night; that would be going to an extreme. If sleep comes, very good; sleep. If sleep does not come, allow the body to rest by remaining in a recumbent position, and allow the mind to rest by remaining aware and equanimous.

...

Firstly, you will need less time for sleep.

The Discourse Summaries
Mental impurities inducing sleepiness:

Another enemy is laziness, drowsiness. All night you slept soundly, and yet when you sit to meditate, you feel very sleepy. This sleepiness is caused by your mental impurities, which would be driven out by the practice of Vipassana, and which therefore try to stop you from meditating. You must fight to prevent this enemy from overpowering you. Breathe slightly hard, or else get up, sprinkle cold water on your eyes, or walk a little, and then sit again.

The Discourse Summaries
On involuntary action during sleep:

Unconscious actions are, however, still regarded as morally motivated, but should be
  understood to differ from involuntary actions or reactions. Sue Hamilton, for example, discusses the
  possibility of involuntary reactions and how it is accounted for:

I have suggested that if one is not conscious of a sound then one has not heard it. We
    can, however, sometimes react ―involuntarily‖ to a sound without being conscious of it: in sleep,
    for example, a loud sound can cause one to make a movement even if there is absolutely no consciousness
    of the sound at all. We also experience peripheral awareness which we do not seem to
    be conscious of. We regularly avoid obstacles in our path while our attention is wholly elsewhere,
    for example. Though such experiences of peripheral awareness might indicate the minimal level
    to which consciousness of, or awareness, operates, this question is not explicitly dealt with in the
    Sutta Piaka. Nor is the experience of involuntary reactions explained. This is a significant omission
    because involuntary reactions such as wet dreams became the subject of controversy in the
    early Buddhist sangha: if they are unconscious, do they constitute a volition with moral implications?


Source: The Unconscious
Though not in a Buddhist perspective this course also might be of some interest: Sleep: Neurobiology, Medicine, and Society

7141: <p>What are the proper relax / Sleep practices for a practitioner of meditation methods?</p>

<p>As to Buddhist point of view what is sleep and how to cope with it?</p>
 -1: <p>As Suminda wrote <a href="https://buddhism.stackexchange.com/a/12988/382">in his answer</a>, eleven benefits of freedom of mind through <em>metta</em> are listed by the Buddha, among them:</p>

<blockquote>
  <p>"One sleeps easily, wakes easily, dreams no evil dreams."<br>
  --<a href="http://www.accesstoinsight.org/tipitaka/an/an11/an11.016.than.html" rel="nofollow noreferrer">AN 11.16</a></p>
</blockquote>

<p>More generally, the Buddha has said he sleeps at ease even in unpleasant circumstances because he abandoned craving, aversion and delusion (<a href="http://www.accesstoinsight.org/tipitaka/an/an03/an03.034.than.html" rel="nofollow noreferrer">AN 3.34</a>).</p>

<p>He also said about monks in training:</p>

<blockquote>
  <p>"These three things lead to the falling away of a monk in training. Which three? There is the case where a monk in training enjoys activity, delights in activity, is intent on his enjoyment of activity. He enjoys chatter, delights in chatter, is intent on his enjoyment of chatter. <strong>He enjoys sleep, delights in sleep, is intent on his enjoyment of sleep</strong>. These are the three things that lead to the falling away of a monk in training.</p>
  
  <p>"These three things lead to the non-falling away of a monk in training. Which three? There is the case where a monk in training doesn't enjoy activity, doesn't delight in activity, isn't intent on his enjoyment of activity. He doesn't enjoy chatter, doesn't delight in chatter, isn't intent on his enjoyment of chatter. <strong>He doesn't enjoy sleep, doesn't delight in sleep, isn't intent on his enjoyment of sleep</strong>. These are the three things that lead to the non-falling away of a monk in training."</p>
  
  <p>-- <a href="http://www.accesstoinsight.org/tipitaka/kn/iti/iti.3.050-099.than.html" rel="nofollow noreferrer">Iti 3.30</a></p>
</blockquote>

<p>In <a href="http://www.accesstoinsight.org/tipitaka/an/an07/an07.058.than.html" rel="nofollow noreferrer">AN 7.58</a> the Buddha instructs Ven. Maha Moggallana on how to overcome his drowsiness:</p>

<blockquote>
  <p>"Well then, Moggallana, whatever perception you have in mind when drowsiness descends on you, don't attend to that perception, don't pursue it. It's possible that by doing this you will shake off your drowsiness.</p>
  
  <p>"But if by doing this you don't shake off your drowsiness, then recall to your awareness the Dhamma as you have heard &amp; memorized it, re-examine it &amp; ponder it over in your mind. It's possible that by doing this you will shake off your drowsiness.</p>
  
  <p>"But if by doing this you don't shake off your drowsiness, then repeat aloud in detail the Dhamma as you have heard &amp; memorized it. It's possible that by doing this you will shake off your drowsiness.</p>
  
  <p>"But if by doing this you don't shake off your drowsiness, then pull both your earlobes and rub your limbs with your hands. It's possible that by doing this you will shake off your drowsiness.</p>
  
  <p>"But if by doing this you don't shake off your drowsiness, then get up from your seat and, after washing your eyes out with water, look around in all directions and upward to the major stars &amp; constellations. It's possible that by doing this you will shake off your drowsiness.</p>
  
  <p>"But if by doing this you don't shake off your drowsiness, then attend to the perception of light, resolve on the perception of daytime, [dwelling] by night as by day, and by day as by night. By means of an awareness thus open &amp; unhampered, develop a brightened mind. It's possible that by doing this you will shake off your drowsiness.</p>
  
  <p>"But if by doing this you don't shake off your drowsiness, then — percipient of what lies in front &amp; behind — set a distance to meditate walking back &amp; forth, your senses inwardly immersed, your mind not straying outwards. It's possible that by doing this you will shake off your drowsiness.</p>
  
  <p>"But if by doing this you don't shake off your drowsiness, then — reclining on your right side — take up the lion's posture, one foot placed on top of the other, mindful, alert, with your mind set on getting up. As soon as you wake up, get up quickly, with the thought, 'I won't stay indulging in the pleasure of lying down, the pleasure of reclining, the pleasure of drowsiness.' That is how you should train yourself.</p>
</blockquote>

<p>His last advice above is a general instruction on how to sleep and how the Buddha himself is described sleeping. He also describes elsewhere (<a href="http://www.accesstoinsight.org/tipitaka/an/an04/an04.037.than.html" rel="nofollow noreferrer">AN 4.37</a>) how a monk is "devoted to wakefulness":</p>

<blockquote>
  <p>"And how is a monk devoted to wakefulness? There is the case where a monk during the day, sitting &amp; pacing back &amp; forth, cleanses his mind of any qualities that would hold the mind in check. During the first watch of the night, sitting &amp; pacing back &amp; forth, he cleanses his mind of any qualities that would hold the mind in check. During the second watch of the night, reclining on his right side, he takes up the lion's posture, one foot placed on top of the other, mindful, alert, with his mind set on getting up [either as soon as he awakens or at a particular time]. During the last watch of the night, sitting &amp; pacing back &amp; forth, he cleanses his mind of any qualities that would hold the mind in check. This is how a monk is devoted to wakefulness.</p>
</blockquote>
 631: <p>Monks, eleven advantages are to be expected from the release (deliverance) of heart by familiarizing oneself with thoughts of loving-kindness (metta), by the cultivation of loving-kindness, by constantly increasing these thoughts, by regarding loving-kindness as a vehicle (of expression), and also as something to be treasured, by living in conformity with these thoughts, by putting these ideas into practice, and by establishing them. What are the eleven?</p>

<ol>
<li>"He sleeps in comfort. 2. He awakes in comfort. 3. He sees no evil dreams. 4. He is dear to human beings. 5. He is dear to non-human beings. 6. Devas (gods) protect him. 7. Fire, poison, and sword cannot touch him. 8. His mind can concentrate quickly. 9. His countenance is serene. 10. He dies without being confused in mind. 11. If he fails to attain arahantship (the highest sanctity) here and now, he will be reborn in the brahma-world.</li>
</ol>

<p><a href="http://www.accesstoinsight.org/tipitaka/an/an11/an11.016.piya.html" rel="noreferrer">(Mettanisamsa Sutta)</a></p>
 295: <blockquote>
  <p>What are the proper relax / Sleep practices for a practitioner of meditation methods?</p>
</blockquote>

<p>If you do <a href="http://www.dhammasukha.org/metta-barebones-booklet.html" rel="nofollow noreferrer">Metta</a> meditation before sleeping you are better off, as one benefit of Metta is you sleep well. (<a href="http://www.themindingcentre.org/dharmafarer/wp-content/uploads/2010/02/30.6-Attha-Mettanisamsa-S-a8.1-piya.pdf" rel="nofollow noreferrer">(Aṭṭha) Mettânisansa Sutta</a>, <a href="http://www.themindingcentre.org/dharmafarer/wp-content/uploads/2009/12/2.15_Ekadasa_Mettanisamsa_S_a11.16_piya.pdf" rel="nofollow noreferrer">(Ekā,dasa) Mettânisansa Sutta</a>)</p>

<blockquote>
  <p>As to Buddhist point of view what is sleep and how to cope with it?</p>
</blockquote>

<p>This is when your <a href="https://en.wikipedia.org/wiki/Bhavanga" rel="nofollow noreferrer">Bhavanga</a> is active and the revolutions of the Dependent Origination cycles has momentarily stopped. (<a href="http://dhammadownload.com/File-Library/Mogok/TheDoctrineOfPaticcasamuppada-By-UThanDaing.pdf" rel="nofollow noreferrer">The Doctrine of Paticcasamuppada - The Law Of Independent Origination - By U Than Daing</a>, page 32). An essay "<a href="http://www.themindingcentre.org/dharmafarer/wp-content/uploads/2009/12/17.8b-The-unconscious.-piya.pdf" rel="nofollow noreferrer">The Unconscious</a>" by Piya Tan discusses action action that done when sleeping.</p>

<p>--</p>

<p>Thoughts of others on the subject of sleep:</p>

<p><em>On deep sleep and bhavanga:</em></p>

<blockquote>
  <p>The idea of an underlying skilful base to the mind is developed further in the
  Abhidhamma, which analyses the constituents of consciousness in detail. For a
  human rebirth to have occurred, the bhavakga, or consciousness to which the
  mind returns at rest, is skilful, whether with the two roots of non-greed and nonhatred,
  or more usually, with three roots, of wisdom, non-greed and non-hatred.
  This consciousness will be present whenever the mind enters bhavakga, either
  momentarily at the end of each thought-process, or <strong>during deep sleep</strong>. For all born
  as humans, the state of bhavakga is a reflection of the skilful state of mind that
  must have been present at the moment of death as a governing factor for the
  relinking consciousness. It is passive, however, and this predisposition needs
  active cultivation during waking life. Only when skilful consciousness is present
  during daily life, or during meditation, does the mind become actively bright and
  radiant. According to the theory this happens, for instance, at the moment of
  giving, of being alert and interested or when practising jhana: the active part of
  the thought-process ( javana) is then free from defilements. Those practising
  meditation are ‘bringing into being’ a consciousness which is thought to be a kind
  of birthright, but which needs cultivation. In Buddhist countries the human realm
  is considered particularly important for spiritual work. Birth in heaven realms is
  pleasant but lacks the suffering to encourage spiritual work; the realms of
  animals, ghosts and hell beings are considered far too painful for the path, and it
  is difficult, though not impossible, for such beings to find a skilful rebirth. It is
  said that the Buddha always has a human birth as his last existence after many
  lifetimes spent preparing to teach others. One sutta compares rebirth in a hell
  realm as entering into a pit of coals, that of a heaven realm to a stay in a luxurious
  mansion. The human realm, however, is like a man sitting in the shade of a
  tree in a hot climate, also the classic conditions for the practice of meditation
  (see M I 76–7).</p>
</blockquote>

<p>Source: <a href="http://www.ahandfulofleaves.org/documents/Buddhist%20Meditation%20An%20anthology%20from%20the%20Pali%20canon_Sarah%20Shaw.pdf" rel="nofollow noreferrer">Buddhist Meditation: An anthology from the Pali canon</a>, by <a href="http://www.orinst.ox.ac.uk/staff/isa/sshaw.html" rel="nofollow noreferrer">Sarah Shaw</a></p>

<p><em>On reduced need of sleep for meditations</em></p>

<blockquote>
  <p>Similarly, when you go to bed at night, close your eyes and feel sensation anywhere within the body. If you fall asleep with this awareness, naturally as soon as you wake up in the morning, you will be aware of sensation. Perhaps you may not sleep soundly, or you may even remain fully awake throughout the night. This is wonderful, provided you stay lying in bed and maintain awareness and equanimity. The body will receive the rest it needs, and there is no greater rest for the mind than to remain aware and equanimous. However, if you start worrying that you are developing insomnia, then you will generate tensions, and will feel exhausted the next day. Nor should you forcefully try to stay awake, remaining in a seated posture all night; that would be going to an extreme. If sleep comes, very good; sleep. If sleep does not come, allow the body to rest by remaining in a recumbent position, and allow the mind to rest by remaining aware and equanimous.</p>
</blockquote>

<p>...</p>

<blockquote>
  <p>Firstly, you will need less time for sleep.</p>
</blockquote>

<p><a href="http://www.vridhamma.org/The-Discourse-Summaries" rel="nofollow noreferrer">The Discourse Summaries</a></p>

<p><em>Mental impurities inducing sleepiness:</em></p>

<blockquote>
  <p>Another enemy is laziness, drowsiness. All night you slept soundly, and yet when you sit to meditate, you feel very sleepy. This sleepiness is caused by your mental impurities, which would be driven out by the practice of Vipassana, and which therefore try to stop you from meditating. You must fight to prevent this enemy from overpowering you. Breathe slightly hard, or else get up, sprinkle cold water on your eyes, or walk a little, and then sit again.</p>
</blockquote>

<p><a href="http://www.vridhamma.org/The-Discourse-Summaries" rel="nofollow noreferrer">The Discourse Summaries</a></p>

<p><em>On involuntary action during sleep:</em></p>

<blockquote>
  <p>Unconscious actions are, however, still regarded as morally motivated, but should be
  understood to differ from involuntary actions or reactions. Sue Hamilton, for example, discusses the
  possibility of involuntary reactions and how it is accounted for:</p>
  
  <blockquote>
    <p>I have suggested that if one is not conscious of a sound then one has not heard it. We
    can, however, sometimes react ―involuntarily‖ to a sound without being conscious of it: in sleep,
    for example, a loud sound can cause one to make a movement even if there is absolutely no consciousness
    of the sound at all. We also experience peripheral awareness which we do not seem to
    be conscious of. We regularly avoid obstacles in our path while our attention is wholly elsewhere,
    for example. Though such experiences of peripheral awareness might indicate the minimal level
    to which consciousness of, or awareness, operates, this question is not explicitly dealt with in the
    Sutta Piaka. Nor is the experience of involuntary reactions explained. This is a significant omission
    because involuntary reactions such as wet dreams became the subject of controversy in the
    early Buddhist sangha: if they are unconscious, do they constitute a volition with moral implications?</p>
  </blockquote>
</blockquote>

<p>Source: <a href="http://www.themindingcentre.org/dharmafarer/wp-content/uploads/2009/12/17.8b-The-unconscious.-piya.pdf" rel="nofollow noreferrer">The Unconscious</a></p>

<p>Though not in a Buddhist perspective this course also might be of some interest: <a href="http://ai.umich.edu/portfolio/sleep-neurobiology-medicine-and-society/" rel="nofollow noreferrer">Sleep: Neurobiology, Medicine, and Society</a></p>
