Up to four in 10 people suffer from sleep paralysis at some point in their lives. This terror-inducing experience occurs when a person on the border between wakefulness and sleep gains partial consciousness. The dreamer may perceive that a menacing, oftentimes-otherworldly intruder is in their room or bed, yet they are incapable of moving or screaming—even as the creature begins choking, crushing, raping or attacking them. Scientists believe it's all a hallucination, but in the throes of an attack, sleep paralysis' demons can be deeply convincing.
Baland Jalal, a psychiatry researcher at the University of Cambridge, who has written here about the neuroscience of sleep paralysis, finds the phenomenon "one of the most interesting in medicine."
"Sleeping is such a basic thing, yet while sleeping you might end up questioning your self and world," he says. "You might wonder, 'Do we have a soul? Who am I? Are there outsiders from other plants here? Have I been visited by a supernatural being—a ghost or a demon?'"
Accounts of nocturnal visits from menacing creatures date back time immemorial across virtually all cultures and found in many literary works. But it wasn't until the late 1800s when Silas Weir Mitchell, a surgeon who aided Civil War soldiers, provided some of the first formal descriptions of the condition. Research substantially picked up in the late 1980s, however, when scientists began investigating the neurological, psychological and cultural aspects of the phenomenon. Sleep paralysis, they found, occurs during REM stage of sleep, when most vivid dreaming occurs, and most of the body is temporarily paralyzed (perhaps to prevent us from acting out dreams). If some anomaly occurs in the REM mechanisms and we actually wake up before this sleep phase is complete, then sleep paralysis can ensue.
"It's a pretty troubling event for at least a portion of the people who have the disorder," says Allan Cheyne, a retired cognitive psychologist, formerly at the University of Waterloo. "They might think it was demonic possession or alien abduction, the beginnings of a stroke, incipient psychosis that's going to get worse or that they're never going to come out of the paralysis."
Why the phenomenon occurs in some people but not others—or why someone who has gone their entire life free from sleep paralysis suddenly starts experiencing it—is a cloudier question. "I had two graduate student who both had their first sleep paralysis experiences after beginning their research on that subject, so it seems like it is something that can be primed," Cheyne says. "I suspect that almost anyone can have this experience if conditions are right."
Previous research has found that trauma or depression and sleep paralysis tend to go hand-in-hand, likely because anxiety causes general disruption to sleep, which heightens the chances that something will go wrong in that process and trigger a sleep paralysis event. On the other hand, however, researchers wonder if extreme fear of sleep paralysis itself—either suffered by an individual or an entire culture—might also feed into a vicious cycle of episodes.
Jalal is investigating this hypothesis in cultures around the world. In his latest study, described in the Journal of Nervous and Mental Disease, he and co-author Devon Hinton of Harvard Medical School focused on a group of 100 college students in Cairo. In Egypt, up to 71 percent of the population that experiences sleep paralysis attributes the experience to supernatural forces, nearly half of which believe the Jinn — evil creatures with roots in Islamic mythology—are to blame. Many also believe that such nocturnal attacks can be fatal.
Jalal and Hinton asked the students about their experience with sleep paralysis as well as whether they suffered from symptoms of anxiety, extensive worrying or post-traumatic stress disorder. Forty-three percent of the students—86 percent of them women—said they had experienced sleep paralysis at least once, and of that group 24 percent said they had experienced four or more episodes over the previous year.
Those who experienced sleep paralysis, and especially those who experienced hallucinations, the researchers found, were more likely to suffer from symptoms of PTSD, anxiety or worry. The findings were correlational, however, so for now it's impossible to tease out whether trauma, worry and anxiety cause sleep paralysis, or the other way around—or perhaps a bit of both. Other researchers have uncovered similar relationships, however, including one study that reported 49 out of 100 Cambodian refugees visiting a psychiatric clinic had had a sleep paralysis event in the past year, and that those with PTSD suffered from such attacks most often.
"The fact that experiencing hallucinations during sleep paralysis was associated with higher symptoms of anxiety, trauma and worry may possibly suggest that such hallucinations may drive these symptoms or perhaps even cause them," Jalal says. "But we cannot infer causality from this study."
Interestingly, though, only 11 percent of the Egyptian students said they believed a Jinn was responsible for the attacks. Jalal points out, however, that university attendees might feel embarrassed admitting they believed in such things (likewise, the heavy sex ratio, with more women reporting the condition than men, might also be a reporting bias). And regardless of personal beliefs, he adds, the socio-cultural framework of a person's country—in this case, one that strongly supports the notion of evil spirits—can still exert quite a strong influence. When Cheyne was in the grips of his early sleep paralysis experiences, for example, his first thought was of the supernatural, a connection his brain likely made because of the overriding influence of North American culture. "People in Western societies immediately make the connection to something demonic," he says. "I certainly did, even though I have absolutely no religious sensibilities."
This isn't the first time Jalal has found evidence of such "cultural priming," which can seemingly work for or against sleep paralysis. In Denmark, for example, belief in religion and the supernatural is exceptionally low. In a study published in Culture, Medicine and Psychiatry, Jalal and Hinton found that Danish people were significantly less likely to experience sleep paralysis than Egyptians, who reported three times as many episodes as the Danes. Egyptians also suffered from longer periods of sleep paralysis-induced immobility and a greater fear of dying during the episode, which was in turn strengthened by a person's belief in a supernatural cause.
The studies' findings tie into the idea that culture can create a fearful landscape ripe for sleep paralysis. "If your grandmother tells you that when you go to sleep you might be attacked and strangled by a demon, you're more likely to ruminate about this creature," Jalal says. "That only makes you more likely to have anxiety that causes you to have more hallucinations and episodes. It's a positive feedback loop."