Sleep paralysis

How it works

During REM sleep, the stage where most dreaming happens, the brainstem switches off the muscles of the body. This stops you from acting out your dreams⁴. In sleep paralysis, your mind wakes up before that switch is turned back on¹. You are aware. You can breathe and move your eyes. You cannot move your limbs or speak.

An episode lasts seconds to a few minutes. It ends on its own, or when someone touches you or you manage to move¹. Because the brain is still partly in REM, dream content leaks into the room. Common experiences are a sense of a presence, pressure on the chest, a shadowy figure, or a buzzing sound¹. One explanation is that you cannot breathe deeply in REM sleep, and your brain reads this as a weight¹. Episodes are more common in people who sleep on their back, and after lost sleep, an erratic sleep schedule, or stress¹.

How common it is

The figures come from different kinds of studies. A 2011 systematic review put lifetime prevalence in the general population around 8%¹. Surveys of students, who tend to keep irregular sleep, find a higher figure near 28%¹. A 2024 meta-analysis combining many studies from around the world put the overall figure near 30%³. The spread partly reflects who was surveyed: students and psychiatric patients report more episodes than the general population¹. Online communities, such as r/Sleepparalysis, carry many first-hand accounts that match the presence, pressure, and shadowy-figure pattern seen in the survey data⁵.

Is it a problem?

No. It is not a stroke, not a seizure, and not possession. Breathing continues on its own the whole time¹. It does not damage the brain. Episodes become rarer with a regular sleep schedule, enough sleep, and sleeping on your side¹. During an episode, focus on moving one finger or toe. Small movements often break it.

See a doctor if:

• episodes happen several times a week,
• you also fall asleep suddenly during the day,
• you also go weak when you laugh.

That combination can be narcolepsy, which is treatable¹⁶.

History and culture

Nearly every culture has a name for this. In Newfoundland it is the Old Hag, who sits on the sleeper’s chest². In Japan it is kanashibari, “bound in metal”². Medieval Europe blamed a demon called the incubus². The painting “The Nightmare” by Henry Fuseli, from 1781, shows a creature crouched on a sleeping woman¹. Some researchers think modern reports of alien abduction describe the same experience¹.