Research suggests that cultural beliefs about the phenomenon of sleep paralysis may make it more terrifying to experience, Scientific American reports.

Sleep paralysis is caused by what appears to be a basic brain glitch at the interface between wakefulness and rapid eye movement (REM) sleep. During REM, you have intensely lifelike dreams. To prevent you from acting out these realistic dreams (and hurting yourself!), your brain has a clever solution: it temporarily paralyzes your entire body. Indeed, your brain has a “switch” (a handful of neurochemicals) that tilts you between sleep and wakefulness. Sometimes the “switch” fails, however—your brain inadvertently wakes up while your body is still under the “spell” of REM paralysis, leaving you stuck in a paradoxical state between parallel realities: wakefulness and REM sleep. During sleep paralysis, the crisp dreams of REM “spill over” into waking consciousness like a dream coming alive before your eyes—fanged figures and all.

These hallucinations—often involving seeing and sensing ghostly bedroom intruders—are interpreted differently around the world. In Egypt, sleep paralysis is often thought to be caused by a jinn (“genie”)—a supernatural creature that terrorizes and sometimes kills its victims. In Italy, some interpret sleep paralysis as an assault by the so-called Pandafeche, a figure described as a malevolent witch or terrifying giant cat. In South Africa, Indigenous people believe the state to be caused by segatelelo (black magic), involving menacing dwarflike creatures called tokoloshe, and in Turkey, it is the karabasan—mysterious spirit-like creatures. In contrast, the Danes offer a less imaginative explanation: they largely attribute sleep paralysis to physiological risk factors such as stress.

These explanations—scientific and sensationalist—can have a profound impact on how people experience sleep paralysis. When directly comparing the phenomenon in Egypt and Denmark, we found that Egyptians fear it much more than Danes do. In fact, more than 50 percent of Egyptians who experienced the condition were convinced that sleep paralysis was deadly. Egyptians also believed that the episodes lasted longer—and remarkably, they occurred three times more often for this group. Beliefs about sleep paralysis among Egyptians appeared to have dramatically shaped their experience. Those who attributed it to supernatural forces suffered greater fear of the experience and longer paralysis. A pattern was revealing itself. Paired with particular beliefs, sleep paralysis had gone from a simple “brain glitch” to a chronic, prolonged and potentially fatal supernatural event.

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