You need eight hours of sleep each night
Not everyone needs eight hours of sleep a night. Some people run fine on six while others can barely function without nine. In fact, there's historical evidence that humans used to sleep in intervals: two hours at dusk, a two-hour waking period, and then a second sleep. The amount of sleep you need varies on a variety of factors, including illness, stress, physical activity, and more. As a good rule, if you awake feeling tired, you probably need more or better sleep.