Some researchers are now questioning the idea of a long uninterrupted sleep, says David N. Neubauer, MD, an associate professor at Johns Hopkins University School of Medicine. There's some evidence to show that in darker, earlier times, before LEDs or wall sconces, people tended to sleep in two phases. "Sleep historians like A. Roger Ekirch
have found that people would sleep deeply for half the night, get up and do things for an hour or so, then fall back to sleep for a few more hours," says Neubauer. Some lab studies have supported this: One study from the 1990s showed that when people were kept in the dark for 14 hours, they fell into a similar pattern of a two-phase sleep. So if you happen to be one of those people who sleeps, wakes, pays bills, then sleeps again, Neubauer says you shouldn't assume there's something wrong with you (if you're still getting seven to eight hours and you're not zonked during the day, of course).