Sleep Paralysis: Medical Explanation

“I couldn’t move and I could continuously hear a disorienting buzzing sound in the room but I could not turn to look at it because I couldn’t move, I struggled, I couldn’t cry for help and I could sense a weight on my chest like someone was sitting on it. It was like being awake in a nightmare and I told no one because I thought that there was some kind of demon that came to menace me but people wouldn’t believe me.”

Khyaak - The Demon Of The Dark

One of the commonest experiences of sleep paralysis (once called Old Hag Syndrome) has been quoted above. In its simplest form, sleep paralysis is a condition in which people wake from sleep to find that they are unable to move. In Nepal, experiences similar to that of sleep paralysis are often reported and ascribed to covering of the body by Ghost of the dark “Khyaak” during sleep. Constantly reported about for thousands of years, different cultures at different parts of the world have different figures associated with such kind of experiences. What makes “sleep paralysis” interesting is the fact that it has been associated several uncanny phenomenon like alien abduction, angelic or demonic visitations. Now let us look at it from the perspective of Medical science to make it more interesting. I will not make in truth claims here and leave it for you, dear readers to decide if the explanation makes sense.


Medically, sleep paralysis is a common condition characterized by the inability to perform voluntary muscle movements occuring either during sleep onset (hypnagogic form) or upon awakening (hypnopompic form) and can often be accompanied by hallucinatory experiences. An attack of sleep paralysis is usually harmless and self-limited. It tends to be over in a minute or two as soon as the brain and body re-establish connections and the person is able to move again. It is most commonly associated with nacrolepsy, a neurological condition causing excessive uncontrollable sleepiness and sleep episodes occuring at anytime of the day. In the absence of nacrolepsy, sleep paralysis is termed as Isolated Sleep Paralysis (ISP) which occurs in otherwise healthy individuals and in some cases can be familial as well.

Classical symptom tetrad of Nacrolepsy:

  1. Excessive day time sleepiness
  2. Cataplectic attacks (sudden loss of muscle tone triggered by emotional stimuli like anger, fear, etc.)
  3. Sleep paralysis
  4. Hypnagogic and Hypnopompic hallucinations

Understanding normal sleep pattern:

The depth of sleep changes periodically. During sleep, your body alernates between orthodox or NREM (Non-Rapid Eye Movement) sleep and paradox or REM (Rapid Eye Movement) Sleep and the depth of sleep gradually increases with the beginning of NREM sleep. One cycle of NREM and REM sleep constitutes a sleep rhythm is repeated every 90 to 120 minutes and approximately 5 to 6 times within one night. NREM sleep occurs first and takes upto 75% of your overall sleep time. REM sleep is referred as paradoxical sleep because while the brain and other body systems becomes active (eye movement, accelerated respiratory and heart rate, rise in blood pressure, etc.), muscles become more relaxed. Dreaming usually occurs during each REM phase of sleep due to increased brain activity but only the last dream that took place before spontaneous awakening is remembered. Muslce atonia during dreaming state prevents our body from acting out your dreams.

Relation of REM Sleep with Sleep paralysis:

In a book “Speaking of Sleeping Problems” by Dietrich Langen, he explains about hypnagogic hallucinations:

Sensations occuring during sleep onset consist of optical or acoustic sensory experiences that are not the result of any external stimulus. They include flashes of light, colored rings, waves and other geometric figures, partly disfigured or fragmentary. Whole scenses with action sequences similar to visions also occur. Acoustic phenomenon include the perception of voices, hearing one’s name called or hearing entire fragments of conversation or music.

Sleep paralysis occurs in transition between wakefulness and sleep or vice-versa . The difference from normal REM sleep is that the REM atonia persists but waking consciousness is largely retained in sleep paralysis i.e. your brain is partially conscious and partially in dreamy state and often external environmental stimuli can be remembered. It may be either, a rational mind trying to make sense of dream sensations or a dreamy mind trying to percieve environmental stimuli but the hallucinations often turn horrific due to the fear that sets in due to paralysis.

Here is an Interview with Dr. Irshaad Ebrahim from London Sleep Center to asnwer your sleep paralysis related questions:

  1. What is sleep paralysis?
  2. Can sleep paralysis have long-term effects?
  3. Does sleep paralysis affect many people?
  4. At what stage of sleep does sleep paralysis occur?
  5. How can you treat sleep paralysis?
  6. What is happening to the brain during sleep paralysis?


  1. Demon like Khyaak, Succubus or Incubus sitting on a chest
  2. Out of Body Experience (OBE) expained by Astral projection or travelling (separation of soul from the body during sleep)
  3. Alien abduction

And in the end, few tips regarding prevention and treatment of sleep paralysis:

  1. Improve sleeping habits as it is frequently associated with chronic sleep deprivation, sleep disruptions and irregular sleeping schedule.
  2. Avoid stress and alcohol as they can lead to irregular sleep schedule and sleep disruptions.
  3. Sleeping by lying on sides as sleep paralysis is mostly experienced in supine position (lying on back).
  4. Medications for treatment of depression may be needed.
  5. Evaluation and treatment of nacrolepsy may be needed.
  1. June 23, 2010
  2. June 24, 2010
    • March 16, 2013
      • May 22, 2016
    • December 20, 2017
  3. September 6, 2010
  4. September 10, 2010
    • September 10, 2010
  5. January 2, 2011
  6. February 10, 2011
  7. July 29, 2011
  8. September 4, 2012
    • March 16, 2013
  9. January 11, 2013
  10. November 25, 2013

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