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Sleep Paralysis is a Literal Nightmare

"I couldn't move my limbs. I thought I was going to die."
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Back in 2006, neuroscientist Baland Jalal found himself lying awake in bed, paralyzed from head to toe. "My eyes were open but I couldn't move my limbs. Something evil was pressing on my chest, strangling me, and my legs were being pulled up and down—I thought I was going to die."

Jalal was experiencing sleep paralysis—a freaky sleep phenomenon that occurs during the REM cycle of your slumber. Terrified and fascinated by the experience, he spent the next 10 years trying to get to the bottom of it.  "We know that during REM sleep, our brain blocks the motor neurons that allow us to move, essentially paralyzing the body so that we don't act out our dreams." (Otherwise, most of us would need to sleep in a steel case.) But occasionally—and for reasons scientists don't totally understand—we wake up before those motor neurons have a chance to fire up again, leading to a semi-conscious paralysis that only lasts a few seconds but can feel agonizingly long in the moment.

What Jalal, a neuroscientist at the University of Cambridge, experienced was a classic episode: "People around the world report similar experiences—they hallucinate and see demons, hear whispers, feel pressure on their chest, or think they're floating," he says. Researchers believe that the hallucinations are the result of a short-circuit to your brain's parietal lobe, which is responsible for building your brain's image of your body in space. When you fire off a 'move' command, but the limbs can't go anywhere, those confused signals turn into trippy shadows or out-of-body experiences.

Researchers are still uncertain, however, as to what causes sleep paralysis, which around 20 percent of people have experienced at least once. It's thought that depression and anxiety may play a role. Sleep disorders like narcolepsy or sleep apnea have also been linked to the phenomenon, Jalal adds, as have disruptions to the normal sleep cycle.  But Jalal says one of the biggest contributors to sleep paralysis, ironically, may be fear of the condition itself: "In Egypt, where this [condition] is believed to be caused by an evil genie, people experience three times as many episodes—and more hallucinations—than they do in Denmark, where it's viewed as an odd physiological event."

To date, there's no evidence that sleep paralysis can cause physical harm, nor is it necessarily evidence of a larger health problem, which is about the only good news, seeing as there's no quick trick to escape its clutches.  Jalal says that staying calm—not so easy when you're imagining a gremlin sitting on the edge of your bed—keeping your eyes closed, relaxing your muscles, and meditating on happier thoughts or memories is your best bet for pulling out of the living nightmare.

And between the feelings of having your lungs crushed and limbs go dead, you can at least remind yourself that some poor soul in Egypt probably had it worse than you.