If you often wake up in the middle of the night and can’t fall back asleep right away, you probably call it “insomnia”—but it might actually be more natural than sleeping for eight hours straight. "The dominant pattern of sleep, arguably since time immemorial, was biphasic," a sleep historian tells Life’s Little Mysteries. What that means: Sleep came in two four-hour blocks, with a period of an hour or more in between during which people might pray, think about their dreams, or even visit with neighbors.
But that was back when darkness could last as long as 14 hours a night with nothing but candles for extra light, meaning people were more prone to go to bed early—and thus have more flexibility with their nightly schedule. Thanks to the invention of the lightbulb, we now stay awake later, leaving us with less sleep time—meaning that in order to get the same amount of sleep, we have to do it all at once. But when subjected to natural light patterns, one study found everyone still sleeps biphasically, and concluded that such a sleep pattern is actually beneficial. (Read more sleep stories.)