Jenny Chang / BuzzFeed 1. It feels kind of like you woke up dead. Tap to play or pause GIF Tap to play or pause GIF ABC / Via lostoceanic815.blogspot.com "Most patients say the same thing to describe sleep paralysis: that it feels like you woke up dead. You know that your mind is awake and your body is not — so you're trapped, essentially," Michael Breus, Ph.D., clinical psychologist and fellow of the American Academy of Sleep Medicine, tells BuzzFeed Life. 2. And it's way more complicated than a nightmare. Tap to play or pause GIF Tap to play or pause GIF FX / Via rollergirlsarebatshitcrazy.tumblr.com "It is the complete opposite, actually," Breus explains. When you enter deep REM sleep, your brain tells the body's voluntary muscles to relax and go into almost a state of paralysis, which is called atonia. Atonia actually helps protect the body from injury by preventing you from acting out the physical movements in your dreams. In other parasomnias, such as sleepwalking or REM sleep behavior disorder, atonia does not occur properly and the voluntary muscles move while the mind remains asleep, which is why people can sometimes do crazy things in their sleep and be totally unaware of it. In sleep paralysis, the body remains paralyzed in REM atonia while the brain awakens and the eyes start to open, explains Breus. Sufferers become alert in a transient conscious state, but they are unable to move voluntary muscles or speak. Although involuntary muscle movement, like breathing, is not affected, there is often a sensation of chest pressure, which is why many people wake up from sleep paralysis gasping to take a deep breath. Episodes can last anywhere from 20 seconds to a few minutes. 3. It happens when you're falling asleep or waking up. Tap to play or pause GIF Tap to play or pause GIF cartoonnetwork.com / Via bustle.com Sleep paralysis can occur during one of two transitions in the sleep cycle. The body must go into REM sleep, and it must come out of it, but sleep paralysis occurs when the body has trouble making these transitions. If it happens when you're falling asleep, it's called hypnagogic sleep paralysis, whereas if it happens during waking it's called hypnopompic, Breus explains. Unfortunately, why the body can't transition smoothly is still unknown. 4. Sleep paralysis can involve hallucinations. Chia-Hsin Ho / Creative Commons / Via Flickr: hsinho Unlike the visuals in nightmares or lucid dreams, which occur when the eyes are closed in REM sleep, these hallucinations occur in the state between sleeping and waking when the mind is alert and the eyes are open. True visual and auditory hallucinations during sleep paralysis are relatively rare, according to Breus, but many patients report feeling an undeniably strange or scary presence in the room. Plus, sleep paralysis is just super frightening to begin with, so it often triggers a panicked response with increased heart rate. "People freak out because they can't move, and it's this extreme anxiety which causes people to be very fearful of their surroundings," says Breus. 5. You can't just wake yourself up. Tap to play or pause GIF Tap to play or pause GIF Cinemax / Via stalepopcornau.blogspot.com Some patients report that they can wiggle their toes, fingers, or facial muscles, which helps them wake up the rest of their body. "Everybody tries something different, but you can’t fool mother nature — there's no way to pull yourself out of it. You just have to wait it out," says Breus. 6. Sleep paralysis is actually a natural occurrence and can happen to anyone. Tap to play or pause GIF Tap to play or pause GIF youtube.com / Via mrwgifs.com Every time you go to sleep, there is some risk of waking up in sleep paralysis, says Breus. But severity and degree of consciousness vary greatly — most people have at least one episode at some point in life but aren't even aware of it. When it does happen, it's highly individual and rarely the same experience for everyone. ...But it's most common among young adults and people with a history of mental illness. Tap to play or pause GIF Tap to play or pause GIF Paramount Pictures / Via reactiongifs.com A Penn State study found the highest prevalence rates were in students and psychiatric patients. 7. It's probably related to being sleep deprived. Tap to play or pause GIF Tap to play or pause GIF ABC / Via tumblr.com According to Breus, research has consistently shown that the less sleep you get and the more exhausted you are, the more likely you are to experience sleep paralysis and other sleep disorders. 8. So avoiding sleep paralysis might be as simple as getting better and longer sleep. Tap to play or pause GIF Tap to play or pause GIF Universal Pictures / Via thedailytouch.com "Sleep deprivation can either be measured in quantity or quality," says Breus. "For example, if you have sleep apnea and you wake yourself up because you stop breathing throughout the night, the quantity of your sleep is bad. If you consume large amounts of alcohol, it prevents you from entering deeper stages of sleep which decreases the quality." So if sleep paralysis is something you deal with, make sure you're getting enough sleep and you're not doing things that compromise the quality of your sleep (like drinking a lot or eating right before bed). Breus also suggests noting any abnormal sleep behaviors (that you or your partner may notice), like irregular breathing while sleeping or waking up gasping for air, which could actually be an undiagnosed sleep disorder. 9. But really, there is no definitive cause. Tap to play or pause GIF Tap to play or pause GIF FOX / Via iiamcouture.com Stress, depression, certain prescription medications, and, more recently, an inherited gene have all been linked to sleep paralysis, Breus tells us. But while research shows associations, there is no clear cause of sleep paralysis, which is obviously super frustrating for anyone going through this. We do know that sleep paralysis can either occur on its own as an isolated incident, or it can be a symptom of other sleep disorders, such as narcolepsy. And there's no explanation for why it might happen every other day or just every once in a while. 10. Seriously, people have been trying to explain this weird phenomenon for centuries. Adam Baker / Creative Commons / Via Flickr: atbaker Accounts of sleep paralysis can be found in Persian medical texts dating back to the 10th century. The first clinical observation was made by a Dutch physician in 1664 who diagnosed a 50-year-old woman with "Night-Mare." It was believed to be caused by demons or spiritual possession until the 19th century, when it was termed "sleep palsy" and eventually "sleep paralysis" in medical texts. 11. And it probably explains whatever is going on in this very famous Renaissance painting. Universalimagesgroup / Getty Images / Via gettyimages.com Swiss painter Henry Fuseli's painting is said to be inspired by supernatural dream experiences and the growing interest in sleep paralysis among doctors at the time. This creepy little gremlin could also represent the sensation of chest pressure...or it could be argued that he's just trying to get it in with this sleeping damsel. Hey, girl. Universalimagesgroup / Getty Images / Via gettyimages.com Even the horse in the background is like, "WTF is that?" Universalimagesgroup / Getty Images / Via gettyimages.com 12. People have blamed sleep paralysis on everything from witches and UFOs to giant ghost dogs. Tap to play or pause GIF Tap to play or pause GIF Touchstone / Via watitis95.tumblr.com And there are various folk legends all over the world that attempt to explain the existence of it in different cultures. 13. However, there's really no evidence that it'll kill you. Tap to play or pause GIF Tap to play or pause GIF MTV / Via mtv.tumblr.com "Research has shown that sleep paralysis is not dangerous," says Breus. "It does not cause physical harm to the body and there are no clinical deaths known to date." While there are some terrifying cultural explanations around the world, these are constructed to make sense of a very mysterious condition. "The biggest thing is to educate people to not be afraid," says Breus. "In all likelihood, they just need more rest. If they get enough sleep and the episodes continue with any regularity, then they should go to a sleep disorder specialist." ...But just try telling that to someone who has sleep paralysis. Gravitas Ventures / Via geektyrant.com Anyone who has ever experienced this can tell you that it is effing terrifying and feels almost paranormal, rather than a typical sleep disorder. Sufferers share their frightening experiences in countless YouTube videos, Reddit threads, and sleep paralysis websites. Because no matter what science says, this gremlin is scary AF. Apic / Getty Images / Via gettyimages.com Get it off, get it off!