Why Sleep Paralysis Happens (and How to Prevent It)

October 23, 2020

ou wake up out of a murky sleep and find that you’re unable to move your body, from your forehead all the way down to your little toe. You’re completely paralyzed! You also have a crushing feeling in your chest, as if something heavy is sitting on it, and an uneasy sense that someone’s in the room with you. Your heart pounds and your thoughts spiral as you silently scream inside.

Is this a scene from a great horror movie or something more ominous?

What is sleep paralysis?

Varying cultures have explained this frightening experience in various ways. In Brazilian folklore, a crone with long fingernails skulks on roofs and tramples on sleepers’ chests. In Japanese mythology, vengeful spirits come to suffocate their enemies while they sleep. In contemporary American culture, sleep paralysis has taken on the mythology of alien abductions—sleepers wake up feeling the presence of aliens in the room while experiencing zapping sensations and a feeling of suffocation.

But it turns out this isn’t a slasher flick and you’re not experiencing a haunting. All of these symptoms describe sleep paralysis, a sleep disorder (or symptom of a sleep disorder) that temporarily alters a person’s mobility, perception, thinking, and emotional state during the transition between sleeping and waking.

Sleep paralysis is a fairly common experience—almost 8% of the general population has experienced it at least once. But if you’re a student or someone with a psychiatric diagnosis, your chances of experiencing it go up to almost 1 in 3.

Rest assured, sleep paralysis is usually harmless, especially if it only happens rarely. But why does it happen at all, when is it cause for concern, and how can you prevent it?

Why does sleep paralysis happen?

You’re typically not aware of it, but the “paralysis” part of sleep paralysis actually happens every night when you sleep during rapid eye movement (REM) sleep.

REM sleep is often referred to as a stage of sleep that takes up 20-25% of your typical night. It occurs in a few chunks, mostly during the second half of the night. During REM, your brain is actually quite active—the electrical signals from the brain look almost like they do when you’re awake. This is also when most dreaming happens, along with a lot of emotional processing that the brain does behind the scenes.

While your brain waves may be very active, your body is immobilized during REM. Other than the eyes moving around a lot (hence “rapid eye movement”), your muscles lose tone. This is your body’s way of preventing you from acting out your dreams.

So, every night during REM, you are “paralyzed.” Sometimes, though, the veil between sleep and wakefulness becomes thin and you find yourself straddling both at the same time. Suddenly, you’re awake and helpless while you hallucinate and process emotions. Often, this also comes with a racing heart, fear, and sometimes even a feeling of impending death. No wonder people around the world have mistaken sleep paralysis for a demonic attack!

What makes some people more prone to sleep paralysis?

The good news is that sleep paralysis is usually innocuous. It’s simply a temporary blunder in the sleep-wake brain system that failed to transition you completely from sleep to wakefulness. If it only happens rarely to you, you don’t need to worry.


For those with narcolepsy, a sleep-wake disorder that disrupts a person’s ability to stay awake, sleep paralysis can be a regular experience. Often, narcolepsy comes with not only sleep paralysis when waking, but also hallucinations as one is falling asleep (called “hypnagogic hallucinations”), suddenly falling asleep or losing muscle tone during the day, and having poor nighttime sleep quality. If you experience these symptoms, you should ask your doctor for a referral to a sleep study.

Anxiety and trauma-related disorders

If you experience an anxiety disorder, like panic disorder or social anxiety, you may be at higher risk for sleep paralysis. Having experienced trauma or having post-traumatic stress disorder (PTSD) also makes a person more likely to have sleep paralysis.

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