If you think about evolution, sleep, at some time, was a dangerous undertaking. You lie down in your cave or shelter, and along comes a predator and has you for dinner. Many creatures do not sleep or sleep while standing so they can escape from dangerous situations.
Bernie Siegel is an American writer and retired pediatric surgeon, who writes on the relationship between the patient and the healing process. He is known for his best-selling book Love, Medicine and Miracles.