You may think you don't require much sleep, but you probably need at least seven hours—unless you're part of the 1% to 3% of the population known as “short sleepers." These folks turn in past midnight and get up after just a few hours, brimming with energy—all without the benefit of naps or caffeine. “These people talk fast. They never stop. They're always on the up side of life,” a researcher tells the Wall Street Journal. Though little is known about short sleepers, some studies suggest they may have a mild form of mania known as hypomania.
Scientists haven’t learned a lot about short sleepers: one expert says he’s only found 20 so far. "There aren't nearly as many as there are people who think they're short sleepers," says a psychiatrist. The condition may be genetic: It seems to run in families, and one research team noted a certain gene variation in two subjects, allowing them to genetically engineer short-sleeping mice. Bad news for the rest of us: Scientists say you're either born a short sleeper or you're not; there's no way to turn yourself into one. (Read more sleep stories.)