Insomnia is difficulty in initiating or maintaining sleep or both. An estimated 30% - 50% of the general population are affected by insomnia and 10% have chronic insomnia.

Exposure to stress and psychophysiological reasons may contribute to development of insomnia. Caffeine interferes with falling a sleep and may trigger awakenings. Alcohol medical problems and breathing disorders produce interrupted sleep.

Our biological clock regulates the times of sleep and wake up with a circadian rhythm. It regulates and induces sleep through a mild change in body temperature and mild secretion of certain hormones, melatonin, cortisol and growth hormone. This clock resides in basal brain within the hypothalamus. The rhythm has distinguished pattern within 24 hour. At evening, melatonin secretion increases, muscles relax and body temperature relatively falls to promote the desire to sleep in addition to dim light effect. Quiet restful sleep is essential to peaceful life. The day following a short sleep or sleeplessness night will be difficult one with loss of concentration and danger of exposure to serious mistakes or accidents. Sleeping well is the most important factor underlying the success in learning.