An unpleasant, vivid dream, sometimes accompanied by a sense of suffocation. Nightmares occur during (rapid eye movement) sleep in the middle and later parts of the night, and they are often clearly remembered if the dreamer awakens completely.
Nightmares are especially common in children aged between 8 and 10, and are particularly likely to occur when the child is unwell or anxious. In adults, nightmares may be a side effect of certain drugs, including beta-blocker drugs and benzodiazepine drugs. Repeated nightmares may be associated with traumatic experiences.
Nightmares should not be confused with hypnagogic hallucinations, which occur while falling asleep, nor with night terror, which occurs in (nonrapid eye movement) sleep and is not remembered the next day.... nightmare
n. a false sensory perception of something that is not really there; the perception is subjectively convincing but lacks an external stimulus. Hallucinations may be visual, auditory, tactile, gustatory (of taste), or olfactory (of smell). They may be provoked by mental illness (such as *schizophrenia or severe anxiety disorders), *personality disorders, or physical disorders affecting the brain (such as temporal lobe *epilepsy, sepsis, acute organic syndrome, or stroke) or they may be caused by drugs, alcohol, or sensory deprivation. Hallucinations should be distinguished from dreams and from *illusions (which are misinterpretations of real stimuli). A substantial minority of the population experiences hallucinations not caused by mental illness. Some hallucinations are not always pathological: hypnagogic hallucinations occur in the state between wakefulness and sleep, and the images are often very distinct; these hallucinations occur in 30–60% of patients with *narcolepsy. Hypnopompic hallucinations occur in the state between sleep and full wakefulness; like hypnagogic hallucinations, the experiences may be very vivid.... hallucination
n. an extreme tendency to fall asleep in quiet surroundings or when engaged in monotonous activities. The patient can be woken easily and is immediately alert. It is often associated with *cataplexy, *sleep paralysis, and hypnagogic *hallucinations. One in 2000 individuals may be affected. Narcolepsy is strongly associated with reduced levels of *hypocretin in the cerebrospinal fluid. —narcoleptic adj., n.... narcolepsy
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