Normal human sleep is comprised of two distinct states known as non-rapid eye movement (NREM) and rapid eye movement (REM) sleep.

The aim of this paper is to show the variations of sleep in different psychiatric disorders:

1. 1. Schizophrenia - The complicated interface between psychiatric diagnoses and sleep disturbance is well illustrated in schizophrenia, where the psychiatric symptoms are amplified and aggravated by sleep disruption while at the same time the pathology of schizophrenia may contribute to worsened sleep.

2. 2. Mood Disorders - Sleep complaints are pervasive in those diagnosed with major depressive disorder, including difficulty falling asleep, intermittent awakenings, and early morning awakenings. Most antidepressant medications suppress REM sleep; these agents may also produce alterations in sleep consolidation and sleep architecture.

3. 3. Anxiety Disorders - The cognitive and physiologic changes associated with excessive anxiety alter sleep and are made worse by the lack of sleep.

4. 4. Trauma and Post-traumatic Stress Disorder - Sleep disturbances are common in post-traumatic stress disorder (PTSD). Anxiety dreams, increased REM phasic activity, increased arousals from REM sleep, increased startle response, low dream recall, and possibly elevated awakening thresholds from sleep may characterize PTSD.

5. 5. Alcohol, Alcoholism - Ethanol has been found to have far-reaching effects on sleep and sleep disorders. Individuals with alcoholism commonly have sleep problems.

6. 6. Drugs of Abuse - Nearly all drugs of abuse have considerable effects on sleep and wakefulness and on particular stages of sleep. The sleep stage most typically affected by these drugs is REM sleep.