According to the Cleveland Clinic, sleep paralysis occurs “when your body is in between stages of sleep and wakefulness.” Episodes usually last anywhere from a few seconds to a couple of minutes and are classified as a type of parasomnia. While the experience can be frightening, sleep paralysis is completely harmless.

Researchers estimate that about 30% of people will experience sleep paralysis at least once in their lifetime.

It can happen just as you’re falling asleep or right as you’re waking up. Common symptoms include an inability to move or speak, pressure on the chest, the sensation of being outside your body, vivid hallucinations, and intense fear or panic. Some episodes last only moments, while others can stretch up to 20 minutes.

So what causes it?

During REM sleep—the stage when most dreaming occurs—your brain temporarily “shuts off” your muscles. This prevents you from physically acting out your dreams. Sleep paralysis happens when your mind wakes up before your body does, leaving you conscious but unable to move.

The mismatch is often triggered by:

• High stress
• Poor or irregular sleep
• Anxiety
• Exhaustion
• Disrupted sleep schedules

Several studies have shown that people who are exhausted, stressed, or dealing with sleep deprivation are more likely to experience sleep paralysis, according to sleep expert and CBT psychologist Charlott Ulfsparre.

Despite the fear it brings, sleep paralysis is not dangerous, and it’s not considered a disease. It’s a natural phenomenon that humans have been trying to understand for centuries. Ancient Persian medical texts described it in the 900s, and one of the first documented cases was recorded by a Dutch physician in 1664.

Many cultures developed their own explanations — Japan speaks of being “bound by steel,” Chinese folklore calls it “ghost pressure,” and in parts of Africa it’s described as “a devil riding on your back.”

Some people also experience intense hallucinations. Many describe a presence in the room, someone sitting on their chest, or even an overwhelming feeling of doom. Swedish artist Jonna Jinton has written about her first experience at age 16, describing a strange vibration and the sensation of being pulled into something. Singer Zara Larsson has also spoken openly about her own frightening episodes.

How to prevent sleep paralysis

• Keep a regular sleep schedule
• Reduce stress
• Avoid screens before bedtime
• Create a calm sleep environment

If an episode does happen, try to focus on slow breathing and attempt to move just one finger or toe. Once a tiny bit of movement returns, the rest of your body usually follows.

Sharing information about sleep paralysis can help more people understand what’s happening to them—and reassure them that this disturbing experience is temporary, explainable, and not dangerous.

If you know someone who might benefit from this, please pass it along.