HealthEssentials: Sleep paralysis and sleep hallucinations (also referred to as “sleep demons”) are the results of disrupted sleep.

Still, that doesn’t help quell the fear when they happen. We talked to sleep disorder specialist Alicia Roth, PhD, about what causes these conditions and what you should know if you ever experience them.

The first component of this is sleep paralysis, a condition when a person wakes up but is temporarily unable to move. When it happens, it can feel absolutely terrifying but, Dr. Roth assures us, it is a completely benign condition.

“This happens when there’s a malfunction between REM (rapid eye movement) sleep and wakefulness,” says Dr. Roth. These occurrences, she says, affect about 10% of the population.

Not to be confused with deep sleep, REM sleep is a point in your sleep cycle when your brain is very active. So active, Dr. Roth says, “If we looked at your brain activity on a polysomnography (PSG) during REM sleep, it would look a lot like it does when you’re awake.”

“There are a lot of different things passing through your mind during REM sleep, some of which you remember as dreams,” she continues. “And one of the ways our bodies protect us during this period of REM sleep is to paralyze us so that we don’t act these things out in our sleep.”

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