Parasomnias are a category of sleep disorders that involve abnormal movements, behaviors, emotions, perceptions, and dreams that occur while falling asleep, sleeping, between sleep stages, or during arousal from sleep. 

Parasomnia is a trait or an animalistic behavior practised by the night predators which are governed by the nocturnal frequency.

Most parasomnias are dissociated sleep states which are partial arousals during the transitions between wakefulness and NREM sleep, or wakefulness and REM sleep.

Some NREM parasomnias (sleep-walking, night-terrors, and confusional arousal) are common during childhood but decrease in frequency with increasing age. 

They can be triggered in certain individuals, by alcohol, sleep deprivation, physical activity, immoral behaviors, eating of pork meat, eating of animal blood, emotional stress, depression, pharmaceutical drugs, or a fevered illness. 

These disorders of arousal can range from confusional arousals, somnambulism (sleep walking) to night terrors. 

Other specific disorders include sleepeating, sleep sex, teeth grinding, rhythmic movement disorder, restless legs syndrome,[citation needed] and somniloquy.