What is "sleep paralysis"?
People don't usually notice when they transition between sleep and wakefulness. However, sometimes just before falling asleep or waking up, a person may find themselves aware of what is happening around them but unable to speak or move. They may hallucinate, meaning they experience sensations that aren't actually happening, or feel pressure in their chest. This is a type of sleep disorder, or parasomnia, called sleep paralysis. It's a temporary state that usually doesn't last long — typically from a few seconds to a few minutes. In rare cases, though, it can last up to 20 minutes. Regardless of how long the "paralysis" persists, it can be alarming to experience and may affect normal sleep habits by causing anxiety around sleep.
Also called muscle atonia, sleep paralysis happens as a person is entering or leaving REM sleep. During REM, signals from the brain relax muscles in the arms and legs, preventing too much movement during dreaming. In an episode of sleep paralysis, wakefulness occurs while a sleeper's voluntary muscle control is still offline, causing the person to feel paralyzed.
It's not clear what causes sleep paralysis, but it has been associated with certain mental health conditions, such as anxiety disorders and post-traumatic stress disorder (PTSD). Compared to the general public, sleep paralysis is also more common in people with narcolepsy, a condition that causes daytime sleepiness and bouts of sleep that occur suddenly and without warning. Disrupted sleep patterns or the use of certain medications, such as those for treating attention-deficit/hyperactivity disorder (ADHD), are also linked to sleep paralysis risk.
Estimates about how common sleep paralysis is vary widely. In one study of more than 400 people in Italy, about 40% reported experiencing sleep paralysis at least once. Other estimates suggest that the number of people worldwide who undergo sleep paralysis at least once in their lifetime is closer to 8%, with women affected slightly more frequently than men.
