For an entire summer, Serena, 23, would wake up to a demon with red eyes watching her from the corner of her bedroom. She wasn't dreaming — at least, not exactly. Serena suffers from sleep paralysis. "I always tried to wake up by wiggling my toes and fingers, but it never worked," she says. "I'm convinced my house is haunted."
Although her story may seem freaky, Serena is not alone. Around 8% of the population experiences sleep paralysis at some point in their lives, according to psychologists at Penn State. Episodes are different for everyone. Some people, like Serena, sense a "ghostly presence" or demon hovering around them or in their rooms. Other sleep paralysis sufferers on Reddit describe not being able to breathe, intense pressure on their chest, and auditory hallucinations.
"Sleep paralysis is the result of a mismatch in your sleep cycles," Hope Bastine, a sleep psychology expert, previously told Refinery29. "During REM sleep your body is paralyzed to stop you from acting out your dreams and to carry out essential maintenance. The paralytic substance usually wears off just as we wake up for 3 to 20 minutes after each sleep cycle. However, with a sufferer, they wake up before the paralytic substance has worn off and often when the dreaming state has not quite finished."
During an episode, people feel awake — but they're unable to move, and they may see things that aren't really there, or feel things that aren't really happening.
"People who experience sleep paralysis can have vivid hallucinations because they're dreaming," Steven Bender, DDS, director of the Center for Facial Pain and Sleep Medicine and clinical assistant professor with the Texas A&M College of Dentistry, said in an article for ScienceDaily. "People have felt like they're levitating or that someone is in their bedroom or a variety of other strange experiences, like alien abductions."
The sensation that there's someone in a room with you is called an “intruder” hallucination, according to an article published in Frontiers in Human Neuroscience. The authors say this may happen when someone is experiencing a glitch in their mirror neurons, which fire off when you move or when you watch another person move. During sleep paralysis, activity in these neurons could make you think you're catching sight of someone or something moving, when you're really not.
The details of what you're seeing — say, a demon with red eyes — might just be your brain trying to explain these "movements." "Adding original features, scenarios or stories to try and make sense of what you’re experiencing is a very human thing to do," Baland Jalal, a neuroscientist at the University of California, told The Guardian. "And this is why people see ghosts, demons, aliens or even figments from their past."
The National Health Service of the U.K. says that ways you can prevent sleep paralysis are getting enough sleep (ideally six to eight hours each night), going to bed at the same time each night, and getting regular exercise. The NHS advises not to eat a big meal, smoke, drink alcohol or caffeine before bedtime, and avoid sleeping on your back. They also recommend seeing a general practitioner if your sleep paralysis continues and if it's affecting your day-to-day life — a GP may be needed to treat a possible underlying condition.