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What Causes Sleep Paralysis

Triggers Include Sleep Deprivation, Sleeping on Back


Updated May 16, 2014

Written or reviewed by a board-certified physician. See About.com's Medical Review Board.

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Sleep paralysis is a relatively common experience, but what causes it? Are there things you can do to avoid having sleep paralysis? What are some of the unscientific explanations of the phenomenon?

The causes of sleep paralysis are surprisingly mundane, despite the elaborate explanations given by some people.

Understanding the Causes of Sleep Paralysis

It is estimated that one in three people will experience sleep paralysis at some point in their lives. To better understand what sleep paralysis is, imagine there are two states of consciousness: being asleep and being awake. There is normally a transition period between these states. Elements of consciousness may be preserved - such as an awareness of your environment - while aspects of sleep may begin (such as dreaming). Typically, this transition is brief and uneventful. However, a prolonged or disrupted transition may predispose you to the unusual experiences of sleep paralysis.

In particular, sleep paralysis is believed to relate to a problem regulating rapid eye movement (REM) sleep. It is during REM that our body is paralyzed, so that we are unable to act dreams out. This muscle relaxation, called atonia, may sometimes occur while you are awake. As such, you will be unable to move, even if you are conscious. This is one of the common features of sleep paralysis.

Clearly there are certain triggers of sleep paralysis. It often occurs during periods of sleep deprivation and stress. Many people experience it when their sleep schedule is disrupted, no matter the reason.

Those with shift work sleep disorder may be at increased risk. In addition, it is possible to trigger sleep paralysis experimentally by disrupting REM. There also appears to be a strong association with anxiety and depressive disorders. The use of alcohol or other drugs may also provoke an attack of sleep paralysis. For some people, a family history of sleep paralysis becomes evident, though a genetic cause of the condition is not known.

Most people with sleep paralysis report that it occurs when they are sleeping on their backs (a supine sleeping position). However, less frequently, others have reported it occurring when sleeping on their stomachs or sides as well. The vast majority of people suggest that sleep paralysis happens while falling to sleep (a hypnagogic phenomenon), yet it can also occur when awakening from sleep. It typically occurs at night, but it has also been known to occur during daytime naps.

How to Avoid Sleep Paralysis

If these are some of the causes of sleep paralysis, how can you avoid it? Perhaps the most important thing you can do is to follow the better sleep guidelines. It is necessary to keep a regular sleep schedule, ensure that you get adequate sleep and avoid any of the above triggers that you have identified as being important for you.

For most people, sleep paralysis occurs rarely, but if it occurs more frequently and you find it particularly bothersome, you may wish to speak to your doctor. With a few other symptoms, it might be the sleep disorder narcolepsy. Even if your sleep paralysis occurs in isolation, if it has become disruptive to your life, treatment options are available.

Unscientific Explanations of Sleep Paralysis

Sleep paralysis has occurred throughout recorded history, and there are countless examples in literature and art of the phenomenon. In some parts of the world, the condition is called the "old hag."

Many people describe the experience in religious terms. Some might blame a ghost, demon or devil as the cause. The terrifying elements of sleep paralysis are easily ascribed to a malevolent presence. Others suggest it is due to aliens. There is no scientific evidence for such beliefs.

Others worry that another medical or mental-health problem may be to blame. The list of potential medical maladies that might explain the experience of sleep paralysis is diverse, ranging from seizures to heart attacks to strokes. Some even think they have died. Still other people worry that they have gone insane and do not discuss it because they are worried how others might react to their experience. The episode of sleep paralysis is self-limited without lasting consequences, and so these explanations are proven to be false.

Finally, some people worry that sleep paralysis is just a dream or nightmare. This may actually be the closest to the truth. As described above, sleep paralysis occurs when there is a breakdown between the states of consciousness and sleep, when our dream state intrudes upon our wakefulness.

Fortunately, many people are reassured by a better understanding of the phenomenon of sleep paralysis, so that if it recurs they know how to interpret the experience and can more easily tolerate it until it inevitably ends.


Kryger, M.H. et al. "Principles and Practice of Sleep Medicine." ExpertConsult, 5th edition, 2011.

McCarty, D.E. et al. "A case of sleep paralysis with hypnopompic hallucinations." Journal of Clinical Sleep Medicine. 2009;5(1):83-84.

Morton, K. "Paralyzed at Night: Is Sleep Paralysis Normal?" Stanford Sleep & Dreams. 2010.

Takeuchi, T. et al. "Isolated sleep paralysis elicited by sleep interruption." Sleep. 1992;15:217-225.

Takeuchi, T. et al. "Factors related to the occurrence of isolated sleep paralysis elicited during a multiphasic sleep-wake schedule." Sleep 2002;25:89-96.

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