Parasomnia is a category of sleep disorders characterized by abnormal, undesirable, or unusual behaviors, experiences, or physiological events that occur during sleep, during specific sleep stages, or during the transitions between sleep and wakefulness. The term comes from the Greek “para” (beside or beyond) and the Latin “somnus” (sleep), reflecting the idea that these phenomena occur alongside or outside of normal sleep. Parasomnias can be broadly divided into those arising from non-REM (NREM) sleep and those arising from REM sleep. NREM parasomnias occur predominantly during deep sleep (slow-wave sleep) in the first half of the night and include sleepwalking (somnambulism), sleep talking (somniloquy), night terrors, confusional arousals, and sleep-related eating disorder. During NREM parasomnias, the person is typically in a mixed state of sleep and wakefulness and has little or no memory of the episode. REM sleep parasomnias, which occur in the latter part of the night when REM sleep predominates, include REM sleep behavior disorder (in which the normal muscle paralysis of REM sleep is absent, allowing the person to physically act out their dreams), nightmares, and sleep paralysis. REM sleep behavior disorder is of particular clinical concern as it can cause injury and is often associated with neurodegenerative conditions such as Parkinson’s disease. Parasomnias are relatively common in children and tend to decrease with age. Triggers include sleep deprivation, stress, fever, alcohol, and certain medications. While most parasomnias are benign, some can pose safety risks and warrant medical evaluation, particularly when they are frequent, distressing, or potentially harmful.