It shows a woman with her arms thrown below her, in deep sleep as she undergoes a nightmare as an almost hidden horse (the "night-mare") looks on as a demonic and ape-like incubus crouches on her chest.

Although Fuseli had unsuccessfully exhibited at the Royal Academy of London many times earlier, critics reacted with horrified fascination when it was shown at his 1782 showing, and the Nightmare became his first commercially successful work.

[3] Her brilliant colouration is set against the darker reds, yellows and ochres of the background; Fuseli used a chiaroscuro effect to create strong contrasts between light and shade.

The work was likely inspired by the waking dreams experienced by Fuseli and his contemporaries, who found that these experiences related to folkloric beliefs like the Germanic tales about demons and witches that possessed people who slept alone.

In these stories, men were visited by horses or hags, giving rise to the terms "hag-riding" and "mare-riding", and women were believed to engage in sex with the devil.

The early meaning of nightmare included the sleeper's experience of weight on the chest combined with sleep paralysis, dyspnea, or a feeling of dread.

According to the art critic Nicholas Powell, the woman's pose may derive from the Vatican's Ariadne, and the style of the incubus from figures at Selinunte, an archaeological site in Sicily.

[12] Fuseli painted other versions; the original was sold for twenty guineas, while an engraving by Thomas Burke circulated widely from January 1783, earned the publisher John Raphael Smith more than 500 pounds.

Fuseli wrote of his fantasies to Lavater in 1779: "Last night I had her in bed with me—tossed my bedclothes hugger-mugger—wound my hot and tight-clasped hands about her—fused her body and soul together with my own—poured into her my spirit, breath and strength.

Anthropologist Charles Stewart characterises the sleeping woman as "voluptuous,"[15] and one scholar of the Gothic describes her as lying in a "sexually receptive position.

[18] One version of The Nightmare hung in the home of Fuseli's close friend and publisher Joseph Johnson, gracing his weekly dinners for London thinkers and writers.

In these scenes, the incubus afflicts well known subjects such as Napoleon Bonaparte, Louis XVIII, British politician Charles James Fox, and Prime Minister William Pitt.

The iconic imagery associated with the Creature's murder of the protagonist Victor's wife seems to draw from the canvas: "She was there, lifeless and inanimate, thrown across the bed, her head hanging down, and her pale and distorted features half covered by hair.

[24] His narrator compares a painting in Usher's house to a Fuseli work, and reveals that an "irrepressible tremor gradually pervaded my frame; and, at length, there sat upon my heart an incubus of utterly causeless alarm".