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What Is Sleep Paralysis: Causes, Risk Factors, And Prevention

Causes And Risk Factors Of Sleep Paralysis

Sleep paralysis is a sleep disorder that occurs during falling asleep and waking up due to an overlap between wakefulness and sleep. You are conscious in this state but can't move, speak, or react and often hallucinate. Episodes usually last for a few seconds to minutes and are frightening. It's more common in students and psychiatric patients and is often a symptom of narcolepsy. A consistent sleep schedule and a light meal before bed can prevent it.

Have you ever woken up and felt stuck to your bed, unable to move your limbs? There seemed to be someone in the room, watching you, advancing toward you menacingly, sometimes even drawing the sheets away. You couldn’t breathe! Someone was sitting on your chest! And though you wanted to scream, you couldn’t even whisper. You just lay there, terrified, waiting for the unimaginable to happen. Then you were suddenly released or you woke up or even drifted back to sleep.

No, this is not a visit from malevolent spirits or evil aliens. The medical term for this phenomenon is sleep paralysis.

If you are temporarily unable to move, speak, or react during sleep onset or upon waking up, you are undergoing sleep paralysis. You may even have visual or auditory hallucinations.

Sleep Paralysis

Sleep paralysis is medically defined as a temporary inability to move, speak, or react during waking up or falling asleep despite being in a state of consciousness. It is a sleep disorder that falls under the category of parasomnia or unusual behavior during sleep.1 Based on the time when it occurs, it can be categorized as:

  • Hypnagogic or predormital – when falling asleep
  • Hypnopompic or post-dormital – when waking up

You may experience sleep paralysis either during falling asleep or while waking up. If it occurs mostly during falling asleep, get checked for narcolepsy.

If sleep paralysis occurs independently of sleep disorders like narcolepsy (a chronic brain disorder where the brain has poor control on the sleep-wake cycle) or other medical conditions, it is called isolated sleep paralysis. If it occurs repeatedly, it is known as recurrent isolated sleep paralysis.

Who Gets Sleep Paralysis?

You aren’t the only one suffering from sleep paralysis. A study on 36,533 participants found that

  • 7.6% of the general population

    Students, psychiatric patients, Asian people, and women experience sleep paralysis more than their counterparts do.

  • 28.3% of students
  • 31.9% of psychiatric patients

experienced at least one episode of sleep paralysis.

The study also found that Asians (38.7%), especially Asian students, were most likely to experience sleep paralysis, and women (18.9%) were more likely victims of recurrent sleep paralysis than men (15.9%).2

Though sleep paralysis begins mostly during adolescence, there have been cases of onset in childhood or middle age.3

Frequency And Duration

In most people, isolated sleep paralysis episodes occur less than once a year and the episodes last for a few seconds to minutes. But in those with recurrent sleep paralysis, the episodes are more frequent and last for several minutes, and the phenomenon might continue for months. As per the International Classification of Sleep Disorders (ICSD), it can be thus categorized on the basis of frequency and duration:4


  • Mild: Episodes occur less than once per month
  • Moderate: Episodes occur more than once per month but less than weekly
  • Severe: Episodes occur at least once per week


  • Acute: 1 month or less
  • Subacute: More than 1 month but less than 6 months
  • Chronic: 6 months or longer

Causes Of Sleep Paralysis

As you begin to fall asleep, your body starts relaxing, taking you through the 4 stages of the non-rapid eye movement (NREM) phase, eventually lulling you into deep sleep. After 80 to 100 minutes, you move into the rapid eye movement (REM) phase, where you start dreaming vividly. You keep repeating this NREM/REM cycle till you wake up.

During the dream phase or the REM phase of your sleep, your brain paralyzes your muscles so that you don’t act out the dreams.

During REM, your brain releases chemicals called glycine and GABA to paralyze your muscles5 so that you don’t physically act out the dreams. This state is called atonia. Your brain is highly active; your breathing is irregular; and your heart rate and blood pressure are high.6

While Falling Asleep

If you start dreaming as soon as you begin to fall asleep, it causes overlap between wakefulness and sleep, causing hypnagogic sleep paralysis.

Sometimes, however, you drift off to REM sleep quickly, skipping NREM. This is known as sleep onset REM. Hypnagogic sleep paralysis occurs in this stage. If this phenomenon is recurrent, it suggests narcolepsy.

While Waking Up

Hypnopompic sleep paralysis occurs when you wake up before the REM stage is complete. This is due to an overlap in sleep states or an overlap between wakefulness and sleep. This can happen if:7

Nerves that make you sleep are hyperactive and those that wake you are underactive. So your brain delays in releasing your muscles.

  • The group of nerve cells responsible for sleep – the REM sleep-on neurons – are hyperactivated.
  • Or the group of nerve cells responsible for wakefulness and/or non-REM sleep – the REM sleep-off neurons – are underactive. This is because melatonin, the sleep hormone that regulates the sleep-off neurons, becomes lowest during REM sleep.8
  • Or both these occur together.

You have woken up, but your brain has not released the muscles and is still in the dream state. Hence the bizarre hallucinations and experiences that often accompany sleep paralysis.

Sleep Paralysis Hallucinations

There are usually 3 kinds of visual hallucinations, also called hypnagogic hallucinations, that accompany sleep paralysis.

1. Intruder

Sleep paralysis patients report sensing someone else's presence in the room.

You feel that there is a threatening presence in the room. Some people even report seeing shapes, animals, or tall, dark, formless bodies.9

When your senses become hyper-aroused in your sleep, you hallucinate about a threatening presence during sleep paralysis.

A 1999 study claims that this is due to a hypervigilant state initiated in the midbrain.10 Hypervigilance is a state where your senses are highly enhanced to enable you to detect the slightest threat. Such heightened sensitivity also brings along anxiety, which explains the fear associated with such experiences during sleep paralysis.

2. Incubus

When you are experiencing sleep paralysis, it might feel as though someone is choking you.

You feel that someone is sitting on your chest and suffocating you.

Obstructions in breathing causes a pressure in the chest, which triggers panic and makes you hallucinate about someone choking you.

Breathing is anyway shallow and rapid during REM. And, if you are lying on your back, the upper airway muscles are also relaxed, reducing the airflow. So, as you struggle to breathe deeply and fail, panic sets in, and you interpret the situation as someone sitting on your chest.11

3. Unusual Bodily Experience Or Out-Of-Body-Experience

Often, out-of-body experiences are reported by people who have had sleep paralysis.

The University of Waterloo conducts an interesting survey on the experiences people have during sleep paralysis. In it, some people have reported that they have been able to leave their bodies and float in the air or fly about.

The sensation of floating outside your body is produced when your brain receives information about body movement even though there is no actual movement.

How does this happen? To put it simply, several mechanisms in your body coordinate to give it information about its movement and position. During sleep paralysis, some of these get activated, but in the absence of corresponding movement, your body mistakenly interprets this as floating or flying.12

Sleep Paralysis Risk Factors

1. Sleep Disorders

Patients of narcolepsy, about 17 to 40%,13 are the most usual victims of sleep paralysis. Obstructive sleep apnea, a condition where the throat muscles relax during sleep and obstruct airflow, is also a risk factor.14

Narcolepsy, obstructive sleep apnea, restless leg syndrome, and nighttime leg cramps are all risk factors for sleep paralysis.

If you suffer from any type of sleep disturbance such as caused by restless leg syndrome or even nighttime leg cramps,15 sleep paralysis is likely.

2. Disrupted Sleep-Wake Cycle

Sleeping and waking up follows a 24-hour pattern, the circadian rhythm. When this pattern is disrupted, whether because of alcohol and drug abuse, shift work, inconsistent sleep timings, or lack of sleep,16 the chances of sleep paralysis go up.

3. Genetics

If either of your parents suffers from sleep paralysis, there’s a 50% chance you will too.

Sleep paralysis also runs in the family. A study with siblings and identical and fraternal twins found that genes could be held responsible for 53% of the occurrences of sleep paralysis.17 Identical twins have similar risks of experiencing the condition. And in some cases, sleep paralysis can occur even when the faulty gene is passed on by only one parent.18

4. Trauma

If you have experienced traumatic incidents and you are suffering from post-traumatic stress disorder,19 you are more likely to experience sleep paralysis.

5. Mental Illnesses

If you have a history of panic disorder, anxiety disorder, social anxiety, and a negative self-image, you are likely to hallucinate about an ominous presence – that of an intruder – during sleep paralysis.20 These are often also effects of sleep paralysis itself and the process could be cyclical.

Sleep paralysis is both a cause and an effect of anxiety disorders. It is also related with bipolar disorder and severe depression.

Severe depression is also linked to sleep paralysis.21

People with bipolar disorder also suffer from sleep disturbances and parasomnias.22

6. Sleeping Position

About 60% sleep paralysis episodes occur when one is sleeping on one’s back.

Most incidences of sleep paralysis have been reported in cases where the person was lying on his or her back. The University of Waterloo survey results claim that about 60% of the episodes occur when one is lying in the supine position.23

How To Prevent Sleep Paralysis

Since this condition is triggered naturally by the body and is generally not harmful (unless it is a symptom of narcolepsy or is linked with other mental disorders), there is no medication. If you have recurrent episodes and are traumatized by the experience, visit your doctor. The doctor may prescribe sleeping pills and low doses of antidepressants to help you sleep better. But rather than relying on medication that will have side effects, here’s what you can do:24

Maintain a proper sleep hygiene and do not sleep on your back.

  • Stick to a consistent sleep schedule and ensure that you get enough quality, restorative sleep. Adults usually need 6 to 8 hours of sleep daily.
  • Do not have a large meal or consume alcohol, caffeine, and drugs right before you sleep.
  • Exercise daily but maintain a gap of at least 4 hours between your exercise and sleep.
  • Keep electronic devices away from yourself at least half an hour before sleeping.
  • Don’t sleep on your back or with your hands placed across your chest.

How To Stop Sleep Paralysis

Focus on breathing steadily. Then focus on moving a toe or a finger. Remember that this is just a minor glitch in the body. It will pass.

  • Once you are inside an episode of sleep paralysis, focus on your breathing and try to control it. This will ease off the pressure on the chest.
  • Try making very small movements like moving a finger or wiggling a toe.
  • Also focus on a positive feeling or emotion or a loved person to allay the fear and bring your breathing and heart rate back to normal.25
  • If you have experienced sleep paralysis before, it will be easier for you to remain relaxed and calm. You’d also know that there is nothing paranormal about this and that this will soon be over.

References   [ + ]

1. Sleep Paralysis. NHS Choices
2. Sharpless, Brian A., and Jacques P. Barber. “Lifetime prevalence rates of sleep paralysis: a systematic review.” Sleep medicine reviews 15, no. 5 (2011): 311-315.
3, 4, 13. The International Classification of Sleep Disorders, Revised. American Academy of Sleep Medicine.
5. Brooks, Patricia L., and John H. Peever. “Identification of the transmitter and receptor mechanisms responsible for REM sleep paralysis.” Journal of Neuroscience 32, no. 29 (2012): 9785-9795.
6. The Characteristics of Sleep. Division of Sleep Medicine at Harvard Medical School.
7, 8. Terrillon, Jean-Christophe, and Sirley Marques-Bonham. “Does recurrent isolated sleep paralysis involve more than cognitive neurosciences.” Journal of Scientific Exploration 15, no. 1 (2001): 97-123.
9. The Intruder. University of Waterloo’s Webpage about Sleep Paralysis.
10. Cheyne, J. Allan, Steve D. Rueffer, and Ian R. Newby-Clark. “Hypnagogic and hypnopompic hallucinations during sleep paralysis: neurological and cultural construction of the night-mare.” Consciousness and cognition 8, no. 3 (1999): 319-337.
11. The Incubus. University of Waterloo’s Webpage about Sleep Paralysis.
12. Unusual Body Experiences. University of Waterloo’s Webpage about Sleep Paralysis.
14. Hsieh, Sun-Wung, Chiou-Lian Lai, Ching-Kuan Liu, Sheng-Hsing Lan, and Chung-Yao Hsu. “Isolated sleep paralysis linked to impaired nocturnal sleep quality and health-related quality of life in Chinese-Taiwanese patients with obstructive sleep apnea.” Quality of Life Research 19, no. 9 (2010): 1265-1272.
15. Ohayon, Maurice M., Jürgen Zulley, Christian Guilleminault, and Salvatore Smirne. “Prevalence and pathologic associations of sleep paralysis in the general population.” Neurology 52, no. 6 (1999): 1194-1194.
16. Inugami, Maki, and Timothy I. Murphy MA. “Factors related to the occurrence of isolated sleep paralysis elicited during a multi-phasic sleep-wake schedule.” Sleep 25, no. 1 (2002): 89.
17. Denis, Dan, Christopher C. French, Richard Rowe, Helena Zavos, Patrick M. Nolan, Michael J. Parsons, and Alice M. Gregory. “A twin and molecular genetics study of sleep paralysis and associated factors.” Journal of sleep research 24, no. 4 (2015): 438-446.
18. Mignot, Emmanuel. “Genetics of narcolepsy and other sleep disorders.” The American Journal of Human Genetics 60, no. 6 (1997): 1289-1302.
19. Ohayon, Maurice M., and Colin M. Shapiro. “Sleep disturbances and psychiatric disorders associated with posttraumatic stress disorder in the general population.” Comprehensive psychiatry 41, no. 6 (2000): 469-478.
20. Solomonova, Elizaveta, Tore Nielsen, Philippe Stenstrom, Valérie Simard, Elena Frantova, and Don Donderi. “Sensed presence as a correlate of sleep paralysis distress, social anxiety and waking state social imagery.” Consciousness and cognition 17, no. 1 (2008): 49-63.
21. Szklo‐Coxe, M. A. R. I. A. N. A., Terry Young, Laurel Finn, and Emmanuel Mignot. “Depression: relationships to sleep paralysis and other sleep disturbances in a community sample.” Journal of sleep research 16, no. 3 (2007): 297-312.
22. Harvey, Allison G., Lisa S. Talbot, and Anda Gershon. “Sleep disturbance in bipolar disorder across the lifespan.” Clinical Psychology: Science and Practice 16, no. 2 (2009): 256-277.
23. Preventing and Coping with Sleep Paralysis. University of Waterloo’s Webpage about Sleep Paralysis.
24. Sleep Paralysis. NHS Choices.
25. L. Fredrickson, Barbara, and Robert W. Levenson. “Positive emotions speed recovery from the cardiovascular sequelae of negative emotions.” Cognition & emotion 12, no. 2 (1998): 191-220.


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