user157: I was reading that the Zen monk Hakuin suffered a debilitating condition called zen sickness before his enlightenment. This seem to be a direct result of his practice.
Does anyone know what this was? Has there been a retrospective medical diagnosis of this? Are there equivalent stages of the path in other traditions? Should I be worried?
Thanks

user295: Zen Sickness, by Zen Master Hakuin mentions one cause of it was access striving. In Buddhism you should pratice in a balanced manner. 

Does anyone know what this was? Has there been a retrospective medical diagnosis of this?

From what I have gathered from Zen Sickness this is fatigue due to excessive striving and beyond what the body can bear.
Also possible that this is linked to insight knowledges.

Are there equivalent stages of the path in other traditions? 

Another way these symptoms can have arisen is higher insights: The Progress of Insight - Awareness of Fearfulness to Knowledge of Re-observation
Also some mild forms of restlessness can be due to low level defilements and excessive thinking and pondering about the Dhamma which is mentioned in (Yuga,naddha) Paṭipadā Sutta.

Should I be worried?

Yes if it is excessive striving. No if it insight knowledges.

user11713: The are few borderlines between mystical (enlightenment) and psychotic experiences. 
Read 'Psychotic and Mystical States of Being: Connections and Distinctions', the scholarly paper by Caroline Brett, PhD, in the journal of Philosophy, Psychiatry, & Psychology.
The paper is available free on this website http://www.yogapsychology.org/art_psychoticandmystical.html. Or, if you have access to journals through your library you can download a PDF of Brett's article.)
Brett argues and provides significant evidence that psychotic and mystical experiences (enlightenment states of mind) are fundamentally indistinguishable. She gives some critical distinctions:
"...the psychotic invests the conceptualization of the experience with great emotional significance, because it serves the purpose of contextualizing and reifying the sense of identity, which is under threat."
Before enlightenment: chop wood, carry water; after enlightenment: chop wood, carry water. (Zen proverb)

user-1: Hakuin describes it himself in 'Yasenkanna' - the problem seems to have been that his focus was too cerebral, and the remedy given by the sennin was to direct his energy to his lower body.
https://terebess.hu/zen/Yasenkanna2.pdf

user11661: I think it's basically impossible to know. According to this page, Hakuin, described it as such:

my heart fire began to rise up­ward against the natural course, parching my lungs of their essen­tial fluids. My feet and legs were always ice-cold: they felt as though they were immersed in tubs of snow. There was a constant buzzing in my ears, as if I were walking beside a raging mountain torrent. I became abnormally weak and timid, shrinking and fear­ful in whatever I did. I felt totally drained, physically and mentally exhausted. Strange visions appeared to me during waking and sleeping hours alike. My armpits were always wet with perspira­tion. My eyes watered constantly.

The article includes a footnote explaining some of the context of such claims about "heart fire":

This was a basic notion in Chinese medical lore. Cf. the statement in the encyclopaedic compilation Wu tsa tsu (Five Assorted Offerings, the section on “Man”), by the Ming scholar Hsieh Chao-che: “When a person is engaged in too much intellection, the heart fire burns excessively and mounts upward.”
Torei’s Biography (1710, Age 25) lists twelve morbid symptoms that appeared: firelike burning in the head; loins and legs ice-cold; eyes constantly watering; ringing in the ears; instinctive shrinking from sunlight; irrepressible sadness in darkness or shade; thinking an intolerable burden; recurrent bad dreams sapping his strength; emission of semen during sleep; restlessness and nervousness during waking hours; difficulty digesting food; cold chills unrelieved by heavy clothing.

He lists very specific ailments that are difficult to tie to particular problems connected with meditation practice, and without further accounts from others claiming to have the same thing, how can we know?
Willoughby Britton at Brown University is investigating problems that are arising in people following Mindfulness at the moment, and it's possible that Hakuin's overzealous nature led him to experience what he did (as her research seems to indicate a connection with overly intense practice).
You can read about it here: The Dark Night of the Soul

user5154: I have done some research online and read articles about zen sickness.
There are a couple of problems when doing research, online, on an ailment which, can be "bearing" on enlightenment, because there are lots of  "me too is having this ailment", in other words "I too, am close to being enlightened"; And suddenly, zen sickness symptoms multiplied: psychological depersonalisation, etc.. are linked to zen sickness and the definition of zen sickness becomes vague and fuzzy.
Even when I confine my readings to only very few recorded accomplished zen/chan masters, who actually do intensive meditations, their descriptions of zen sickness differ, and that is perhaps due to incorrect attribution ( the "me too" phenomena) of an experience to zen sickness. (I decided, eventually, not to provide links because it would create more confusion/debate on it, so don't take my word on it). 
The zen sickness of Master Han Shan, IMHO, seems to be a genuine description, but I don't agree to some of the discussion, especially the last but one paragraph which begins with:

The situation of Zen sickness is not something you should desire, and certainly not something you want to force into occurring. Since it is a trouble or affliction, you want to avoid it if you can, but the important thing is that there is a remedy if it occurs. Think of it in terms of ....

It is not something you can force or get into easily unless you want to reprogram your own mind, but that's my view.
Theravada Tradition
From my reading and analysis it would correspond to an Anagami in the Theravada tradition working towards Arahatship, where at that stage the most prominent problem is restlessness.
IMHO, at the path stage of an Anagami it has seen emptiness clearly and enjoys the bliss of holding onto emptiness. To get to the fruit of Anagami it has to let go of that hold on emptiness. Once it has decided to let go of emptiness the bliss, vanished. The bliss makes the mind concentrated, I quote "the purpose of bliss is concentration"(.. in some sutta). 
With the letting go of emptiness & bliss the mind will just grab at any thought,tune,occupations to concentrate the mind, because if it didn't, the restlessness of the mind is unbearable( we are here talking about a very sensitive fine mind; restlessness is one of the last five fetters ).
Why then can not an Anagami phala(phala sounds better than fruit, which reminds me of fruitcake) go back to holding onto emptiness again and get the bliss back? The answer is that it can't, but I won't go into that.
In Theravada we would call it restlessness rather than a (zen) sickness. In the articles on zen sickness I've read, the recommendation is lots of sleep, or get drowsy with alcohol, if permitted, and then get to sleep. But if restlessness is, like I say, unbearable sleep is not an option.
The answer is learning how to abide in emptiness after letting go of emptiness. How to do that is another topic.
The deep state of samadhi in which Master Han Shan was in for 5 days is, in the Theravada tradition equivalent to sanna-vedayita nirodha ( ceassation of perception and feeling) in which when one awakes, enlightenment is gain (but there are controversies, some say back to Anagami phala if it wasn't attained), I haven't a clue!
So it's a bit of way to go before you encounter it and when you encounter it just learn to abide in emptiness, then the restlessness will not go away but lessen. But if you practice jhannas the mind will lead you into sanna-vedayita nirodha for 7 days, like Master Han Shan. The you can tell us about it!

user11753: I would be worried. Happened to me and many other intensive meditators. "Meditation sickness" occurs to those meditators embedded in an ideology or worldview that values silence and stilling thought as superior or as more valuable than thinking or acting. This devalues thought, thinking, and acting in the world. And, these value/devalues are what is associated with "meditation sickness".
Celebrated Zen master Guiding Zongmi, warned that excessive focus on meditation and achieving "inner stillness, and non-critical/non-analytical study of the scriptures led to meditation sickness.
Robert H. Sharf, Professor of Buddhist Studies in the Department of East Asian Languages and Cultures, as well as Chair of the Center for Buddhist Studies, at the University of California, Berkeley, wrote of meditation sickness:

"Meditation sickness" excessive focus in meditation on achieving
  “inner stillness” (ningji), especially when unbalanced by an
  engagement with the scriptures, leads to a state described as “falling
  into emptiness” (duokong), which is, in turn, associated with
  “meditation sickness” (changing). The term meditation sickness was
  used by various Buddhist masters as a critique of practices they
  deemed detrimental to the path, notably techniques that emphasized
  inner stillness—they seem to have been targeting practices that
  cultivated a sort of non-critical or non-analytical presentness." --
  from p476 Is mindfulness Buddhist? (and why it matters), Robert H.
  Sharf, University of California, Berkeley, Transcultural Psychiatry 2015, Vol. 52(4) 470–484


157: <p>I was reading that the Zen monk Hakuin suffered a debilitating condition called zen sickness before his enlightenment. This seem to be a direct result of his practice.</p>

<p>Does anyone know what this was? Has there been a retrospective medical diagnosis of this? Are there equivalent stages of the path in other traditions? Should I be worried?</p>

<p>Thanks</p>
 295: <p><a href="https://buddhismnow.com/2015/09/12/zen-sickness-by-zen-master-hakuin/" rel="nofollow noreferrer">Zen Sickness</a>, by Zen Master Hakuin mentions one cause of it was access striving. In Buddhism you should pratice in a balanced manner. </p>

<blockquote>
  <p>Does anyone know what this was? Has there been a retrospective medical diagnosis of this?</p>
</blockquote>

<p>From what I have gathered from <a href="https://buddhismnow.com/2015/09/12/zen-sickness-by-zen-master-hakuin/" rel="nofollow noreferrer">Zen Sickness</a> this is fatigue due to excessive striving and beyond what the body can bear.</p>

<p>Also possible that this is linked to insight knowledges.</p>

<blockquote>
  <p>Are there equivalent stages of the path in other traditions? </p>
</blockquote>

<p>Another way these symptoms can have arisen is higher insights: <a href="http://www.accesstoinsight.org/lib/authors/mahasi/progress.html" rel="nofollow noreferrer">The Progress of Insight</a> - <a href="http://www.accesstoinsight.org/lib/authors/mahasi/progress.html#ch6.6" rel="nofollow noreferrer">Awareness of Fearfulness</a> to <a href="http://www.accesstoinsight.org/lib/authors/mahasi/progress.html#ch6.13" rel="nofollow noreferrer">Knowledge of Re-observation</a></p>

<p>Also some mild forms of restlessness can be due to low level defilements and excessive thinking and pondering about the Dhamma which is mentioned in <a href="http://www.themindingcentre.org/dharmafarer/wp-content/uploads/2013/04/41.5-Yuganaddha-Patipada-S-a4.170-piya.pdf" rel="nofollow noreferrer">(Yuga,naddha) Paṭipadā Sutta</a>.</p>

<blockquote>
  <p>Should I be worried?</p>
</blockquote>

<p>Yes if it is excessive striving. No if it insight knowledges.</p>
 11713: <p>The are few borderlines between mystical (enlightenment) and psychotic experiences. </p>

<p>Read 'Psychotic and Mystical States of Being: Connections and Distinctions', the scholarly paper by Caroline Brett, PhD, in the journal of Philosophy, Psychiatry, &amp; Psychology.</p>

<p>The paper is available free on this website <a href="http://www.yogapsychology.org/art_psychoticandmystical.html" rel="nofollow noreferrer">http://www.yogapsychology.org/art_psychoticandmystical.html</a>. Or, if you have access to journals through your library you can download a PDF of Brett's article.)</p>

<p>Brett argues and provides significant evidence that psychotic and mystical experiences (enlightenment states of mind) are fundamentally indistinguishable. She gives some critical distinctions:</p>

<p>"...the psychotic invests the conceptualization of the experience with great emotional significance, because it serves the purpose of contextualizing and reifying the sense of identity, which is under threat."</p>

<p>Before enlightenment: chop wood, carry water; after enlightenment: chop wood, carry water. (Zen proverb)</p>
 -1: <p>Hakuin describes it himself in 'Yasenkanna' - the problem seems to have been that his focus was too cerebral, and the remedy given by the sennin was to direct his energy to his lower body.</p>

<p><a href="https://terebess.hu/zen/Yasenkanna2.pdf" rel="nofollow noreferrer">https://terebess.hu/zen/Yasenkanna2.pdf</a></p>
 11661: <p>I think it's basically impossible to know. According to <a href="https://buddhismnow.com/2015/09/12/zen-sickness-by-zen-master-hakuin/" rel="nofollow noreferrer">this page</a>, Hakuin, described it as such:</p>
<blockquote>
<p>my heart fire began to rise up­ward against the natural course, parching my lungs of their essen­tial fluids. My feet and legs were always ice-cold: they felt as though they were immersed in tubs of snow. There was a constant buzzing in my ears, as if I were walking beside a raging mountain torrent. I became abnormally weak and timid, shrinking and fear­ful in whatever I did. I felt totally drained, physically and mentally exhausted. Strange visions appeared to me during waking and sleeping hours alike. My armpits were always wet with perspira­tion. My eyes watered constantly.</p>
</blockquote>
<p>The article includes a footnote explaining some of the context of such claims about &quot;heart fire&quot;:</p>
<blockquote>
<p>This was a basic notion in Chinese medical lore. Cf. the statement in the encyclopaedic compilation <em>Wu tsa tsu</em> (Five Assorted Offerings, the section on “Man”), by the Ming scholar Hsieh Chao-che: “When a person is engaged in too much intellection, the heart fire burns excessively and mounts upward.”</p>
<p>Torei’s Biography (1710, Age 25) lists twelve morbid symptoms that appeared: firelike burning in the head; loins and legs ice-cold; eyes constantly watering; ringing in the ears; instinctive shrinking from sunlight; irrepressible sadness in darkness or shade; thinking an intolerable burden; recurrent bad dreams sapping his strength; emission of semen during sleep; restlessness and nervousness during waking hours; difficulty digesting food; cold chills unrelieved by heavy clothing.</p>
</blockquote>
<p>He lists very specific ailments that are difficult to tie to particular problems connected with meditation practice, and without further accounts from others claiming to have the same thing, how can we know?</p>
<p>Willoughby Britton at Brown University is investigating problems that are arising in people following Mindfulness at the moment, and it's possible that Hakuin's overzealous nature led him to experience what he did (as her research seems to indicate a connection with overly intense practice).</p>
<p>You can read about it here: <a href="https://www.theatlantic.com/health/archive/2014/06/the-dark-knight-of-the-souls/372766/" rel="nofollow noreferrer">The Dark Night of the Soul</a></p>
 5154: <p>I have done some research online and read articles about zen sickness.</p>

<p>There are a couple of problems when doing research, online, on an ailment which, can be "bearing" on enlightenment, because there are lots of  "me too is having this ailment", in other words "I too, am close to being enlightened"; And suddenly, zen sickness symptoms multiplied: psychological depersonalisation, etc.. are linked to zen sickness and the definition of zen sickness becomes vague and fuzzy.</p>

<p>Even when I confine my readings to only very few recorded accomplished zen/chan masters, who actually do intensive meditations, their descriptions of zen sickness differ, and that is perhaps due to incorrect attribution ( the "me too" phenomena) of an experience to zen sickness. (I decided, eventually, not to provide links because it would create more confusion/debate on it, so don't take my word on it). </p>

<p>The <a href="http://www.meditationexpert.com/yoga-kung-fu/y_zen_sickness_of_zen_master_han_shan.htm" rel="nofollow noreferrer">zen sickness of Master Han Shan</a>, IMHO, seems to be a genuine description, but I don't agree to some of the discussion, especially the last but one paragraph which begins with:</p>

<blockquote>
  <p>The situation of Zen sickness is not something you should desire, and certainly not something you want to force into occurring. Since it is a trouble or affliction, you want to avoid it if you can, but the important thing is that there is a remedy if it occurs. Think of it in terms of ....</p>
</blockquote>

<p><strong>It is not something you can force or get into easily unless you want to reprogram your own mind, but that's my view.</strong></p>

<p><strong>Theravada Tradition</strong></p>

<p>From my reading and analysis it would correspond to an Anagami in the Theravada tradition working towards Arahatship, where at that stage the most prominent problem is restlessness.</p>

<p>IMHO, at the path stage of an Anagami it has seen emptiness clearly and enjoys the bliss of holding onto emptiness. To get to the fruit of Anagami it has to let go of that hold on emptiness. Once it has decided to let go of emptiness the bliss, vanished. The bliss makes the mind concentrated, I quote "the purpose of bliss is concentration"(.. in some sutta). </p>

<p>With the letting go of emptiness &amp; bliss the mind will just grab at any thought,tune,occupations to concentrate the mind, because if it didn't, the restlessness of the mind is unbearable( we are here talking about a very sensitive fine mind; restlessness is one of the last five fetters ).</p>

<p>Why then can not an Anagami phala(phala sounds better than fruit, which reminds me of fruitcake) go back to holding onto emptiness again and get the bliss back? The answer is that it can't, but I won't go into that.</p>

<p>In Theravada we would call it restlessness rather than a (zen) sickness. In the articles on zen sickness I've read, the recommendation is lots of sleep, or get drowsy with alcohol, if permitted, and then get to sleep. But if restlessness is, like I say, unbearable sleep is not an option.</p>

<p>The answer is learning how to abide in emptiness after letting go of emptiness. How to do that is another topic.</p>

<p>The deep state of samadhi in which Master Han Shan was in for 5 days is, in the Theravada tradition equivalent to sanna-vedayita nirodha ( ceassation of perception and feeling) in which when one awakes, enlightenment is gain (but there are controversies, some say back to Anagami phala if it wasn't attained), I haven't a clue!</p>

<p>So it's a bit of way to go before you encounter it and when you encounter it just learn to abide in emptiness, then the restlessness will not go away but lessen. But if you practice jhannas the mind will lead you into sanna-vedayita nirodha for 7 days, like Master Han Shan. The you can tell us about it!</p>
 11753: <p>I would be worried. Happened to me and many other intensive meditators. "Meditation sickness" occurs to those meditators embedded in an ideology or worldview that values silence and stilling thought as superior or as more valuable than thinking or acting. This devalues thought, thinking, and acting in the world. And, these value/devalues are what is associated with "meditation sickness".</p>

<p>Celebrated Zen master Guiding Zongmi, warned that excessive focus on meditation and achieving "inner stillness, and non-critical/non-analytical study of the scriptures led to meditation sickness.</p>

<p>Robert H. Sharf, Professor of Buddhist Studies in the Department of East Asian Languages and Cultures, as well as Chair of the Center for Buddhist Studies, at the University of California, Berkeley, wrote of meditation sickness:</p>

<blockquote>
  <p>"Meditation sickness" excessive focus in meditation on achieving
  “inner stillness” (ningji), especially when unbalanced by an
  engagement with the scriptures, leads to a state described as “falling
  into emptiness” (duokong), which is, in turn, associated with
  “meditation sickness” (changing). The term meditation sickness was
  used by various Buddhist masters as a critique of practices they
  deemed detrimental to the path, notably techniques that emphasized
  inner stillness—they seem to have been targeting practices that
  cultivated a sort of non-critical or non-analytical presentness." --
  from p476 <a href="http://buddhiststudies.berkeley.edu/people/faculty/sharf/documents/Sharf%20Is%20Mindfulness%20Buddhist.pdf" rel="nofollow noreferrer">Is mindfulness Buddhist? (and why it matters), Robert H.
  Sharf, University of California, Berkeley, Transcultural Psychiatry 2015, Vol. 52(4) 470–484</a></p>
</blockquote>
