ABSTRACT
Why do we sleep? What happens when we sleep? Do we need to sleep? People have pondered such questions about sleep since ancient times. Aristotle addressed the issue of sleep in his essay “On Sleep and Sleeplessness,” in which he wrote that sleep and waking originate in the heart and are regulated by a primary sense organ. He proposed that after food is eaten, evaporation from it rises to the brain, condenses, and sinks down to the heart, causing sleep (1).
