Although sleep is a daily occurrence for humans, our understanding of it is tragically limited. Ancient humans not only failed to understand sleep but also feared it, worried that they might never wake up. Even more than a hundred years ago, many scholars still believed that sleep was a transitional phase between life and death. With the advancement of medicine, scientists discovered that the human body and its physiological functions do not come to a halt during sleep; instead, the body uses this time to carry out various physiological activities distinct from those of the daytime...