ABSTRACT: Sleep plays a vital role in good health and well-being throughout your life. Getting enough quality sleep at the right times can help protect your mental health, physical health, quality of life, and safety. Sleep initiation and maintenance take place with the function of a lot of cortical and subcortical region of the brain. In the initiation of sleep, it is accepted that primarily cyclic inputs from the hypothalamus and anterior hypothalamus, ventrolateral preoptic nucleus with the signals of endogenous chemical. Normal sleep is divided into two states: rapid eye movement (REM) and non-rapid eye movement (NREM).The major neurotransmitter of REM is acetylcholine and of NREM are GABA and serotonine. In a normal individual, NREM and REM sleep alternate cyclically throughout the night. The NREM-REM cycle repeats itself every 90-110 min, 5-6 times per night. Typically, NREM sleep predominates in the first part of the night, and REM sleep predominates in the second. Sleep disorders can be divided in three groups according to occurence period: (1) Sleep disorders seen in REM, (2) in NREM and (3) in any of REM or NonREM periods. Patients with sleep disorders may effects (road and work accidents), social maladjustment, decreased academic and occupational performance. Thus, sleep disorder is a serious condition that requires investigation, diagnosis and treatment