Here's a classic case of survival of the fittest: While roughly 98 percent of the population needs at least seven to nine hours of sleep a night to maintain good mental and physical health, roughly 2 percent of the population needs just a few hours—and they’re still bouncing with energy. With less hours spent with their head on the pillow and more hours spent getting things done, these superhuman short sleepers have an advantage over the rest of us. But a lot of people who claim to be short sleepers are in fact sleep-deprived: Out of 100 people who say they can get by on less than six hours of sleep, only five of them actually can, says Daniel J. Buysse, former president of the American Academy of Sleep Medicine. On the other hand, the sleepless elite apparently have different circadian rhythms and are generally more positive and thinner than the average person. They are supposedly "energetic, outgoing... and ambitious." They also have a higher tolerance for physical pain and psychological trauma.