It is not clear exactly why the body requires sleep, although inadequate sleep can have severe detrimental effects on health. Studies have shown that sleep is essential for normal immune system function and to maintain the ability to fight disease and sickness. Sleep also is essential for normal nervous system function and the ability to function both physically and mentally. In addition, sleep is essential for learning and for normal, healthy cell growth.
Everyone experiences occasional sleep problems, but getting a good night's sleep is essential for feeling refreshed and alert during the day. Lack of sleep might make you feel foggy and unable to concentrate, or just a lesser version of your normal self. Sleep problems will eventually disrupt your work, family and personal relationships.

There are five stages of sleep that cycle over and over again during a single night's rest. Stage 1 is light sleep during which the muscles begin to relax and a person can be easily awakened. During stage 2, brain activity slows down and eye movement stops. Stages 3 and 4 comprise deep sleep, during which all eye and muscle movement ceases. It can be difficult to wake a person during deep sleep. Stage 3 is characterized by very slow brain waves (delta waves), interspersed with small, quick waves. In stage 4, the brain waves are all delta waves. It is during deep sleep that some people sleepwalk and children may experience bedwetting. It is during REM sleep that dreams occur. The muscles of the body stiffen, the eyes move, the heart rate increases, breathing becomes more rapid and irregular, and the blood pressure rises. About 50% of sleep time is spent in stage 2 and about 20% is spent in REM (normally more than 2 hours a night in adults). A complete sleep cycle, from the beginning of stage 1 to the end of REM, usually takes about an hour and a half.

Insomnia – a short term or chronic inability to get high quality sleep – is a common sleep problem and can be caused by a variety of things including stress, a change in time zones, an altered sleep schedule or poor bedtime habits. Whether your problem is an occasional sleepless night or a series of them, plenty of solutions exist to help you get better sleep.
Sleep apnea is a common sleep disorder that can be potentially very serious, and even life-threatening. In sleep apnea, your breathing stops or gets very shallow while you are sleeping. Each pause in breathing typically lasts 10 to 20 seconds or more, and the pauses can occur 20 to 30 times or more an hour. During the episodes of apnea, the sleeper wakes up to breathe again, disrupting sleep, and also suffers from a brief lack of oxygen.
Restless legs syndrome (RLS) is a disorder causing an almost irresistible urge to move the legs (or arms). The urge to move occurs when resting or lying down and is usually due to uncomfortable, tingly, or creeping sensations in the legs or affected limbs. Movement eases the feelings, but only for a while. Narcolepsy is a neurological disorder that causes extreme sleepiness and may even make a person fall asleep suddenly and without warning. Specific causes of narcolepsy are not known but people with narcolepsy are lacking hypocretin, a brain chemical which regulates sleep and wakefulness.