On average, human beings spend 33 percent of their lives sleeping, according to Sleep Disorders and Sleep Deprivation. This amounts to about eight hours per day. While not everything is known about sleep, it is a critical physiological need of human beings and other animals.
Studies indicate that age has a bearing on how much sleep an individual needs. According to WebMD, babies sleep for 16 to 18 hours per day, teenagers sleep for about nine hours, while adults sleep for seven to nine hours per day. If a person is deprived of sleep, she may suffer from poor memory, depression, impaired immunity and fatigue.