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Why are demons blamed for sleep paralysis?

Incubi, Succubi and Sleep Paralysis
The feet of an incubus from a 1489 woodcut.
The feet of an incubus from a 1489 woodcut.

We tend to think of "nightmares" as mere dreams of a particularly disturbing or frightening power, but the etymology of the word delivers us directly into the terror of sleep paralysis. Mare stems from mara, the Anglo-Saxon word for "crusher," a stark reference to that typical sensation of some entity asquat upon the sleeper's chest.

The maras of Anglo-Saxon folklore were small imps or goblins, much like the squatter in Henry Fuseli's iconic 1781 painting "The Nightmare."Other cultures, both ancient and modern, adapted differing descriptions. In Newfoundland, Canada, the Old Hag suffocates the sleeper with her hideous, hoary bulk, while the Greek Ephialtes leaps upon its slumbering prey like a great and loathsome frog.

Each culture has its own rules and expectations in place for these entities of sleep paralysis, each drawing on different worldviews, fears and supernatural beliefs. Sometimes, there's even a precautionary system in place, such as placing iron nails under your mattress to deter the French Cauchemar or employing a dream-eating Baku in Japan.

While the cultural particulars vary, we can describe most of these maras as demonic in nature. Even the alien abduction experience, which serves as a frequent modern wrapping for the experience, involves a frightening, physical assault by an unearthly being. But one of the more elaborate and overtly sexual maras comes to us from the world of Christian demonology: the ghastly and erotic dance of the incubi and succubi.

The incubus or "that which lies upon" is a masculine, shapeshifting demon that takes the form of an attractive man to engage sexually with a female victim. The succubus or "that which lies beneath," serves as the feminine counterpart, preying upon male victims in the guise of a beautiful woman. In both cases, however, a pair of bestial feet was present to alert faithful Christians to the infernal con.

According to 15th-century Bishop Alonso Tostado, the incubus and succubus were simply two forms of the same demonic entity. Tostado theorized that a succubus lies with a man in order to collect his semen and then morphs into an incubus to fertilize a female with the ill-gotten seed. In other words, it's all an elaborate artificial insemination scheme to produce satanic children.

Demon-on-human sex was a subject of surprising complexity in 15th-century Europe. On one hand, as much as half of the general public experienced sleep paralysis, confounded by sexual dreams and nocturnal emissions in both sexes. Remember, the terror of the sleep paralysis experience is due to combination of combination of situational and individual factors.

Throw in a religious script of sexual impurity and a rich tapestry of witchcraft theory and you have quite a recipe for a scandalous demonic encounter.

Sleep paralysis can prove terrifying. Even a single experience can resonate throughout a person's lifetime, and humans throughout history have aimed to give the malevolent, hallucinatory presence at its heart a name, a cause and a purpose within the fabric of their own worldview.

And thus they glimpse their demon in the dark.