Poet Edward Fairfax kept a 1621 account of his daughter Helen’s terrible nightmares, describing an incident in which she complained about a demonic white cat that “has been long upon me and drawn my breath.” The cat, she said, “has left in my mouth and throat so filthy a smell that it does poison me.”

The practice of yobai, “night crawling,” was common in rural communities in medieval Japan, and continued into the twentieth century. A young man would visit a young woman’s house after dark, disguising his features with a cloth to avoid embarrassment should his advances be rejected. These premarital liaisons could become formal if a child were conceived.

“Darkness has come upon me,” a hymn in the Rig Veda laments. “O Dawn, banish it like a debt.” The morning light is here asked, suggested translator Wendy Doniger, to act as a collection agency—to “make good what darkness had incurred or ‘exact’ the darkness from night as one would exact money.”

Asked whether it was night or day that first emerged when the universe came into existence, sixth-century-bc Greek philosopher Thales of Miletus replied, “Night, earlier by a day.”

A special committee of the U.S. House of Representatives asked Lewis W. Leeds, a ventilation engineer and prominent critic of the popular belief that night air is inherently harmful to humans, to assess air quality inside the Capitol in 1868. The resulting report concluded that the House Chamber “is really the foulest place in the whole building,” with vents “so choked up with tobacco spittal and sweepings of the floor as to render the air rising from them very disagreeable.”

In August 2018 data scientist David Bamman examined how authors recently interviewed in the New York Times’ By the Book column answered the question “What’s on your nightstand?” Women mentioned male and female authors almost equally; men mentioned male authors more than 79 percent of the time. “Don’t read in bed,” advised Fran Lebowitz. “It’s too stimulating. Watch TV instead. It’s boring.”

A study of sixty-two mammalian species found that animals around the world have shifted into more nocturnal lives. “Humans are now this ubiquitous, terrifying force on the planet,” said lead author Kaitlyn Gaynor, “and we are driving all the other mammals back into the night-time.” The Southeast Asian sun bear, formerly diurnal, now spends as much as 70 percent more time awake at night to avoid humans.

Into the early modern period, the word bug referred to a phantom in the dark; a 1535 translation of the Bible made for Henry VIII came to be known as the Bug Bible for its rendering of Psalm 91:5 as “Thou shalt not nede to be afrayed of eny bugges by night.” The word was changed to terrors in later editions, but the original sense still colors the common bedtime warning against letting bedbugs bite.

Psychologists at the University of California recognized a lack of sleep “as a social repellent” and its effect contagious: “People who come in contact with a sleep-deprived individual, even through a brief one-minute interaction, feel lonelier themselves as a result.”