Rapid eye movement sleep, non-rapid eye movement sleep, dreams, and hallucinations.
Current Psychiatry Reports June 1, 2005 Raffaele Manni
Dreaming occurs during both REM and NREM sleep, not only during REM sleep as long thought. Hallucinatory activity during sleep is normal and increases toward morning, becoming equally present in REM and NREM sleep. In narcolepsy, hypnagogic hallucinations arise from a REM-dissociation state where dream imagery intrudes into wakefulness. Similar mechanisms may contribute to visual hallucinations in various neuropsychiatric disorders. Evidence suggests that both REM and NREM processes, including arousal-related processes, play a role in hallucinations, particularly in delirium tremens and Parkinson's disease.