If you’ve ever woken up unable to move or speak — even though your mind was fully awake — you’ve likely experienced something called sleep paralysis.

It’s far more common than most people realize, but because the experience feels surreal and often terrifying, many hesitate to talk about it.

30% of people will experience it

Most people have never heard of a sleep disorder called sleep paralysis. But it’s something many of us will experience at least once in our lives—whether we remember it or not.

Sleep paralysis is a medical condition that occurs in the moments right before you fall asleep or as you’re waking up. During an episode, a person becomes unable to move or speak, even though they’re mentally awake.

It’s also common to experience hallucinations or out-of-body sensations, which makes the situation feel especially frightening.

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.