The human body is affected by regular cycles The human body is affected by regular cycles, like moon phases, tides or even the female menstrual cycle. There is another cycle most people are not aware of called the Circadian Cycle, which affects the body's sleep patterns every 24 hours. The Circadian Cycle is what tells the body when it should rest, and that is in early afternoon (the siesta) and late evening. Modern life, with artificial lighting, caffeine and sugar, allows us to circumvent this natural sleep pattern. When this happens, then the quality of sleep decreases. There are two cycles of sleep; the body first goes in to a light sleep phase and if it not disturbed, it will enter the REM phase of sleep, which is essentially a more therapeutic sleep. During this time, the body heals itself and the individual will awaken felling refreshed.