" aspects of health; even if we manage a full night’s sleep, unless enough of that sleep is in a deep state, we’ll suffer from sleep deprivation. Unlike in rapid eye movement (REM) sleep, in the deep sleep stage, your body and brain waves slow down. This is the stage where information is stored in long-term memory, learning and emotions are processed, the immune system is energized, and the body recovers. Healthy adults spend an average of 13 to 23 percent of their night in deep sleep. So if you sleep for seven hours, that translates to just fifty to one hundred minutes in a deep state. Each minute, in other words, is precious. "

― Greg McKeown , Effortless: Make It Easier to Do What Matters Most