Sleep is defined as unconsciousness from which the person can be aroused by sensory or other stimuli. distinguished from coma, which is unconsciousness from which the person cannot be aroused. There are multiple stages of sleep, from very light sleep to very deep sleep; sleep researchers also divide sleep into two entirely different types of sleep that have different qualities, Sleep-wake cycle refers to our 24 hour daily sleep pattern which consists of approximately 16 hours of daytime wakefulness and 8 hours of night-time sleep. The complex process of the sleep-wake cycle is controlled by the body’s circadian rhythm and sleep homeostasis (the amount of accumulated sleep need that builds during time spent awake).