It's true that there are some people who need just a few hours of sleep each night. However, it's probably not you or me. The numbers are quite small; only an estimated 1 to 3 percent among us can function just fine with only five hours of sleep each night. Short sleepers, nicknamed the "sleepless elite" tend to run in families; it's not that they've somehow trained themselves to need less sleep, though (we'll get to that later). Rather, they carry a gene variation, hDEC2, that allows them to go without, and with no apparent consequence [source: Beck]. The rest of us, well, we just stopped noticing how tired we are.
Too little sleep, though, makes you more than just drowsy. Sleep deprivation is associated with some pretty severe health problems, including obesity, heart disease and diabetes. Get too little sleep -- five hours or fewer per night -- and you double your risk of death from all causes [source: Peri]. And once you've been awake for 18 hours, you may be more than just a little tired. Get behind the wheel of your car at that point, for example, and you could be mistaken for driving under the influence.