Sleep Paralysis: What Happens, and Why

February 13, 2017
Heidi Moawad, MD

Controlled studies have been able to replicate sleep paralysis with sleep interruption, but only in 10% of participants with interrupted REM sleep.

Sleep paralysis is considered an under recognized condition. It can occur in association with other sleep disorders, particularly narcolepsy, but it may also occur independently of other sleep disorders, and in those situations it is identified as isolated sleep paralysis. 

Sleep paralysis is the term used to describe episodes of complete physical paralysis that occur while fully alert and awake.

Description of sleep paralysis episodes 

Sleep paralysis experiences are described as very memorable and unsettling to patients. Affected individuals recall the events vividly, and what distinguishes sleep paralysis from nightmares and night terrors is that affected individuals remember that they were awake during sleep paralysis, but recognize that they were asleep after a nightmare or a night terror is over. 

Sleep paralysis is characterized by an inability to move the muscles while awake. When it is not associated with narcolepsy, sleep paralysis generally occurs in the context of sleep, typically upon awakening from sleep. The event is characterized by an inability to move the body despite being awake. 

Most sufferers describe a strange terror and a sense of being trapped inside their bodies, unable to speak or move, but able to think. After the episode resolves, either after falling asleep for a time period or without getting additional sleep, the affected individual can recall and vividly describe the sense of being physically paralyzed.  

Most patients (about 76%) who experience this phenomena report fear, and about 15% report some degree of distress. There is a strong association with the impression of a ‘presence,’ or a supernatural component, which likely contributes to the distress during, and even after, the episode. 

Why sleep paralysis happens

The reason for these unusual episodes is, strangely, both simple and complicated at the same time. Sleep paralysis is believed to be triggered by interrupted sleep. But not everyone who has interrupted sleep experiences sleep paralysis. It appears that episodes of sleep paralysis occur during waking periods of REM activity and are associated with muscle atonia, which is part of the normal sleeping cycle, but not a usual characteristic of wakefulness. The episodes may be provoked when REM periods occur after waking from sleep. Controlled studies have been able to replicate sleep paralysis with sleep interruption, but not in all participants, and in fact, only about 10% of participants who have interrupted REM sleep in the study setting report sleep paralysis. 

Treatment of sleep paralysis

At this time there is not a widely recommended treatment for sleep paralysis. Given that the trigger may be interruption of sleep during a specific part in the sleep cycle that is not yet clearly defined, it would be almost impossible to predict when a person would unexpectedly experience exactly the type of sleep disruption that could potentially trigger an episode of isolated sleep paralysis. 

However, for those who suffer from repeated episodes, an understanding of the cause of the event, as well as, of course, attempts to get adequate sleep, can help alleviate some of the terror involved with feeling atonic while awake. 

What would you do if a patient complained of supernatural experiences?

Reference: Sharpless BA. A clinician’s guide to recurrent isolated sleep paralysis. Neuropsychiatr Dis Treat. 2016 Jul 19;12:1761-1767.