user-1: Recently sloth and torpor has been a huge hindrance in meditation; my biggest hindrance as it happens. I've managed to reduce the bulk of it but I find that it's still hanging around in some sessions. For the most part, I can see sloth and torpor trying to engulf me and thus am able to take evasive action by refocusing my meditative state. Sometimes though, it gets me even to the point of falling asleep. It's been with me now for months on and off. 18 months previous to this it hasn't really effected me like it has now.
Here are some descriptions of the hindrance in question:
Heaviness of mind, like wading through oil. Tiredness when I don't appear to be tired outside of meditation. Falling asleep. Dullness of mind. Sinking into a gloop.
The Buddha compared it to (I'm paraphrasing here) being imprisoned in a cramped, dark cell, unable to move freely in the bright sunshine outside.
The largely recommended antidote by my sangha is to rouse energy by exerting myself outside of meditation. This has not been helpful or perhaps I'm not receiving the message correctly. It seems to be more of a mind thing and that is the route I'd like to take to address it so I've been sitting and watching and trying to evade it. I just can't seem to eliminate it completely. I have some sessions where I am free of it and some sessions that start out with meditative potential only to be confronted some-way through the session with the dealings of sloth and torpor. 
Things I've tried: bright light from a light box and also from daylight, light exercise before meditation, opening my eyes in mid-session, water on my face before a session.

user43: So... Assuming you're still accepting answers... The traditional methods for overcoming the "sloth and torpor" all involve applying some kind of antidotes opposite to the problem: walking, washing face with cold water, exercise, visualizations of light etc.
In my own experience I've discovered something else. It looks like this type of sleepiness is different from the normal one that happens when one is tired or bored. Indeed, you yourself said that the drowsiness does not exist outside of meditation.
As I observed this phenomenon I got convinced that it has nothing to do with regular "sloth and torpor" and has an entirely different nature. So I watched it carefully. Here is what happens in my case. My mind gets super heavy to the point of blacking out and I just can't maintain it awake however much forceful effort I apply. Then, I can either keep trying to fight it, or give in to it. So I tried giving in - but without stopping my meditation session. What I found is that there was another region of mind - another chunk of my subjective mental space - that was actually fully awake that I could enter! All I had to do is stop boxing myself and holding my attention to the limited region of mind-space - and allow myself to experience mind-space outside of the box.
Based on this experience, my theory is, this phenomenon has to do with the way our attention is managed. It looks like when meditation is actually effective it leads to calming down of thoughts in our habitual region of attention, but we still keep our "manas" attached to the same region it was on during the day, so now with the "lights out" this region is experienced as this heavy sleepy condition.
This is indirectly confirmed by the Tibetan texts on meditation, which say that this sleepy state is actually a stage that indicates that meditation is going well, and that the task of the meditator is to learn to break through.
For me, this break through involves no longer holding to that same region of mind-space that's gone dark, but by relaxing and opening to the other regions of mind. I can't say I've mastered this reliably 100% but I can do it more or less well, so at this point I'm pretty sure this is a real thing and not just my imagination.
You are free to take this with a grain of salt, though you are welcome to try it and see if it works for you. I'd be interested to know if anyone gets the same experience, so we could confirm or deny this.

user14387: Also recently experiencing the challenge of sloth and torpor. All hinderances are actually a great opportunity for our growth, our spiritual evolution and our inner/overstanding of what is in the way, is the way. 
In addition to the traditional suggestions, perhaps checking out if any of the following lines of inquiry concerning sloth and torpor are helpful, wholesome, wise, and skillful:
What is the relationship to the hinderance? How is the hinderance approached and handled? Is conflict with the hinderance present? 
What happens when expanding awareness or switching to a more open awareness practice?
Does rapidly recalling dharma knowledge and teachings aid in dispelling lethargy?
What if it wasn’t sloth and torpor? What if powerful metta is being sent (to what is experienced as (our) consciousness, energy, mental activity and body)? [Recall the behavior of the charging drunken war elephant when encountering metta from the historical Buddha.] What happens when what is perceived as sloth and torpor gives way to allowing and receiving metta, or loving-kindness?
Can sloth and torpor allow for a closer examination of the largely unknown processes and thresholds of hypnagogic and liminal states?
Can employment of the iddhis of engagement, enthusiasm, energy and investigation strengthen vitakka (the continual attending/(re)aiming/(re)applying of attention on/to the meditation object)?
Or can simply changing the (originally chosen) meditation object help?

user-1: 
Mumonkan Case 16: When the Bell Sounds
Unmon said, "The world is vast and wide.  Why do you put on your
  seven-piece robe at the sound of the bell?"  
Mumon's Comment
In studying Zen, you should not be swayed by sounds and forms.  Even
  though you attain insight when hearing a voice or seeing a form, this
  is simply the ordinary way of things. Don't you know that the real Zen
  student commands sounds, controls forms, is clear-sighted at every
  event and free on every occasion?
Granted you are free, just tell me: Does the sound come to the ear or
  does the ear go to the sound? If both sound and silence die away, at
  such a juncture how could you talk of Zen?  While listening with you
  ear, you cannot tell. When hearing with your eye, you are truly
  intimate.
Mumon's Verse
With realization, things make one family;  Without realization,
  things are separated in a thousand ways. Without realization,
  things make one family; With realization, things are separated in
  a thousand ways.

Medhini gives a good gloss of the traditional techniques for overcoming sloth/torpor.  Honestly, I'd try those first before moving into what I'm about to say.
One thing I've noticed in my own practice is that my own sloth and torpor is inversely proportional to my clarity of intention.  What I mean by that is sometimes we take up an object of meditation but don't fully commit to it.  We might focus on the tip of our nose, for instance, but never quite arouse a sense of clear intention.  Our vitaka - our applied thought - is more like someone lazily flopping on a bed.  We just sort of hang out there in a haze of comfortable, quasi-concentration.  And then we promptly fall asleep.
Instead, imagine the intention of a monk putting on his seven piece robe before sitting down for meditation.  Or take a look at this bloke doing some iado:
https://youtu.be/byAgl-b2xFs
That is how you want to approach your concentration object.  Command sound, 
 control form!  Your breath is like a razor sharp sword.  Don't let it escape your attention for even a moment.  Handle it as if your life depended on it!  

-1: <p>Recently sloth and torpor has been a huge hindrance in meditation; my biggest hindrance as it happens. I've managed to reduce the bulk of it but I find that it's still hanging around in some sessions. For the most part, I can see sloth and torpor trying to engulf me and thus am able to take evasive action by refocusing my meditative state. Sometimes though, it gets me even to the point of falling asleep. It's been with me now for months on and off. 18 months previous to this it hasn't really effected me like it has now.</p>

<p>Here are some descriptions of the hindrance in question:</p>

<p>Heaviness of mind, like wading through oil. Tiredness when I don't appear to be tired outside of meditation. Falling asleep. Dullness of mind. Sinking into a gloop.</p>

<p>The Buddha compared it to (I'm paraphrasing here) being imprisoned in a cramped, dark cell, unable to move freely in the bright sunshine outside.</p>

<p>The largely recommended antidote by my sangha is to rouse energy by exerting myself outside of meditation. This has not been helpful or perhaps I'm not receiving the message correctly. It seems to be more of a mind thing and that is the route I'd like to take to address it so I've been sitting and watching and trying to evade it. I just can't seem to eliminate it completely. I have some sessions where I am free of it and some sessions that start out with meditative potential only to be confronted some-way through the session with the dealings of sloth and torpor. </p>

<p>Things I've tried: bright light from a light box and also from daylight, light exercise before meditation, opening my eyes in mid-session, water on my face before a session.</p>
 43: <p>So... Assuming you're still accepting answers... The traditional methods for overcoming the "sloth and torpor" all involve applying some kind of antidotes opposite to the problem: walking, washing face with cold water, exercise, visualizations of light etc.</p>

<p>In my own experience I've discovered something else. It looks like this type of sleepiness is different from the normal one that happens when one is tired or bored. Indeed, you yourself said that the drowsiness does not exist outside of meditation.</p>

<p>As I observed this phenomenon I got convinced that it has nothing to do with regular "sloth and torpor" and has an entirely different nature. So I watched it carefully. Here is what happens in my case. My mind gets super heavy to the point of blacking out and I just can't maintain it awake however much forceful effort I apply. Then, I can either keep trying to fight it, or give in to it. So I tried giving in - but without stopping my meditation session. What I found is that there was another region of mind - another chunk of my subjective mental space - that was actually fully awake that I could enter! All I had to do is stop boxing myself and holding my attention to the limited region of mind-space - and allow myself to experience mind-space outside of the box.</p>

<p>Based on this experience, my theory is, this phenomenon has to do with the way our attention is managed. It looks like when meditation is actually effective it leads to calming down of thoughts in our habitual region of attention, but we still keep our "manas" attached to the same region it was on during the day, so now with the "lights out" this region is experienced as this heavy sleepy condition.</p>

<p>This is indirectly confirmed by the Tibetan texts on meditation, which say that this sleepy state is actually a stage that indicates that meditation is going well, and that the task of the meditator is to learn to break through.</p>

<p>For me, this break through involves no longer holding to that same region of mind-space that's gone dark, but by relaxing and opening to the other regions of mind. I can't say I've mastered this reliably 100% but I can do it more or less well, so at this point I'm pretty sure this is a real thing and not just my imagination.</p>

<p>You are free to take this with a grain of salt, though you are welcome to try it and see if it works for you. I'd be interested to know if anyone gets the same experience, so we could confirm or deny this.</p>
 14387: <p>Also recently experiencing the challenge of sloth and torpor. All hinderances are actually a great opportunity for our growth, our spiritual evolution and our inner/overstanding of what is in the way, is the way. </p>

<p>In addition to the traditional suggestions, perhaps checking out if any of the following lines of inquiry concerning sloth and torpor are helpful, wholesome, wise, and skillful:</p>

<p>What is the relationship to the hinderance? How is the hinderance approached and handled? Is conflict with the hinderance present? </p>

<p>What happens when expanding awareness or switching to a more open awareness practice?</p>

<p>Does rapidly recalling dharma knowledge and teachings aid in dispelling lethargy?</p>

<p>What if it wasn’t sloth and torpor? What if powerful metta is being sent (to what is experienced as (our) consciousness, energy, mental activity and body)? [Recall the behavior of the charging drunken war elephant when encountering metta from the historical Buddha.] What happens when what is perceived as sloth and torpor gives way to allowing and receiving metta, or loving-kindness?</p>

<p>Can sloth and torpor allow for a closer examination of the largely unknown processes and thresholds of hypnagogic and liminal states?</p>

<p>Can employment of the iddhis of engagement, enthusiasm, energy and investigation strengthen vitakka (the continual attending/(re)aiming/(re)applying of attention on/to the meditation object)?</p>

<p>Or can simply changing the (originally chosen) meditation object help?</p>
 -1: <blockquote>
  <p><strong>Mumonkan Case 16: When the Bell Sounds</strong></p>
  
  <p>Unmon said, "The world is vast and wide.  Why do you put on your
  seven-piece robe at the sound of the bell?"  </p>
  
  <p>Mumon's Comment</p>
  
  <p>In studying Zen, you should not be swayed by sounds and forms.  Even
  though you attain insight when hearing a voice or seeing a form, this
  is simply the ordinary way of things. Don't you know that the real Zen
  student commands sounds, controls forms, is clear-sighted at every
  event and free on every occasion?</p>
  
  <p>Granted you are free, just tell me: Does the sound come to the ear or
  does the ear go to the sound? If both sound and silence die away, at
  such a juncture how could you talk of Zen?  While listening with you
  ear, you cannot tell. When hearing with your eye, you are truly
  intimate.</p>
  
  <p>Mumon's Verse</p>
  
  <p>With realization, things make one family; <br> Without realization,
  things are separated in a thousand ways.<br> Without realization,
  things make one family;<br> With realization, things are separated in
  a thousand ways.</p>
</blockquote>

<p>Medhini gives a good gloss of the traditional techniques for overcoming sloth/torpor.  Honestly, I'd try those first before moving into what I'm about to say.</p>

<p>One thing I've noticed in my own practice is that my own sloth and torpor is inversely proportional to my clarity of intention.  What I mean by that is sometimes we take up an object of meditation but don't fully commit to it.  We might focus on the tip of our nose, for instance, but never quite arouse a sense of clear intention.  Our vitaka - our applied thought - is more like someone lazily flopping on a bed.  We just sort of hang out there in a haze of comfortable, quasi-concentration.  And then we promptly fall asleep.</p>

<p>Instead, imagine the intention of a monk putting on his seven piece robe before sitting down for meditation.  Or take a look at this bloke doing some iado:</p>

<p><a href="https://youtu.be/byAgl-b2xFs" rel="nofollow noreferrer">https://youtu.be/byAgl-b2xFs</a></p>

<p><em>That</em> is how you want to approach your concentration object.  Command sound, 
 control form!  Your breath is like a razor sharp sword.  Don't let it escape your attention for even a moment.  Handle it as if your life depended on it!  </p>
