All big animals sleep, but some sleep by day instead of night. When humans do this, that is, work the night shift, they don't feel as well. Humans need about seven hours of sleep out of the twenty-four. Younger ones sleep more; newborns sleep much more. When we are deprived of sleep we are grouchy, think less clearly next day and have less energy. In spite of lots of research at "sleep labs" sleep problems are not understood, except for sleep apnea. Breathing should be even. When breaths are missed it is called apnea. It is especially disturbing when a baby shows apnea.