Note: A more comprehensive classification of sleep disorders is available (International Classification of Sleep Disorders^a), but it should be noted that this is organized differently from ICD-10.
   For some research purposes, where particularly homogeneous groups of sleep disorders are required, four or more events occurring within a 1-year period may be considered as a criterion for use of categories sleepwalking (somnambulism), sleep terrors (night terrors), and nightmares.
Nonorganic insomnia

1. The individual complains of difficulty falling asleep, difficulty maintaining sleep, or nonrefreshing sleep.
2. The sleep disturbance occurs at least 3 times a week for at least 1 month.
3. The sleep disturbance results in marked personal distress or interference with personal functioning in daily living.
4. There is no known causative organic factor, such as a neurological or other medical condition, psychoactive substance use disorder, or a medication.

Nonorganic hypersomnia

1. The individual complains of excessive daytime sleepiness or sleep attacks or of prolonged transition to the fully aroused state upon awakening (sleep drunkenness), which is not accounted for by an inadequate amount of sleep.
2. This sleep disturbance occurs nearly every day for at least 1 month or recurrently for shorter periods of time and causes either marked distress or interference with personal functioning in daily living.
3. There are no auxiliary symptoms of narcolepsy (cataplexy, sleep paralysis, hypnagogic hallucinations) and no clinical evidence for sleep apnea (nocturnal breath cessation, typical intermittent snorting sounds, etc.).
4. There is no known causative organic factor, such as a neurological or other medical condition, psychoactive substance use disorder, or a medication.

Nonorganic disorder of the sleep–wake schedule

1. The individual's sleep–wake pattern is out of synchrony with the desired sleep–wake schedule, as imposed by societal demands and shared by most people in the individual's environment.
2. As a result of disturbance of the sleep–wake schedule, the individual experiences insomnia during the major sleep period or hypersomnia during the waking period, nearly every day for at least 1 month or recurrently for shorter periods of time.
3. The unsatisfactory quantity, quality, and timing of sleep causes either marked personal distress or interference with personal functioning in daily living.
4. There is no known causative organic factor such as a neurological or other medical condition, psychoactive substance use disorder, or a medication.

Sleepwalking (somnambulism)

1. The predominant symptom is repeated (two or more) episodes of rising from bed, usually during the first third of nocturnal sleep, and walking about for between several minutes and half an hour.
2. During an episode, the individual has a blank, staring face, is relatively unresponsive to the efforts of others to influence the event or to communicate with him or her, and can be awakened only with considerable difficulty.
3. Upon awakening (either from an episode or the next morning), the individual has amnesia for the episode.
4. Within several minutes of awakening from the episode, there is no impairment of mental activity or behavior, although there may initially be a short period of some confusion and disorientation.
5. There is no evidence of an organic mental disorder, such as dementia, or a physical disorder, such as epilepsy.

Sleep terrors (night terrors)

1. Repeated (two or more) episodes in which the individual gets up from sleep with a panicky scream and intense anxiety, body motility, and autonomic hyperactivity (such as tachycardia, heart pounding, rapid breathing, and sweating).
2. The episodes occur mainly during the first third of sleep.
3. The duration of the episode is less than 10 minutes.
4. If others try to comfort the individual during the episode, there is a lack of response followed by disorientation and preservative movements.
5. The individual has limited recall of the event.
6. There is no known causative organic factor, such as neurological or other medical condition, psychoactive substance use disorder, or a medication.

Nightmares

1. The individual wakes from nocturnal sleep or naps with detailed and vivid recall or intensely frightening dreams, usually involving threats to survival, security, or self-esteem. The awakening may occur during any part of the sleep period, but typically during the second half.
2. Upon awakening from the frightening dreams, the individual rapidly becomes oriented and alert.
3. The dream experience itself and the disturbance of sleep resulting from the awakenings associated with the episodes cause marked distress to the individual.
4. There is no known causative organic factor, such as neurological or other medical condition, psychoactive substance use disorder, or a medication.

Other nonorganic sleep disorders
Nonorganic sleep disorder, unspecified