Parasomnias are physical, behavioral and experiental phenomena ocurring during entry or along the sleep or on arousal/awakening. The behavior includes movements, emotional, perceptual or dreaming experience, frequently containing manifestations of autonomic nervous system. Parasomnias are devided into primary (ocurring etiher in NREM or REM sleep) and secondary (following organic system disease manifested during sleep). Primary parasomnias are further devided into those that appear during NREM, REM or states of consciousnes that do not respect boundaries between wake and sleep. Parasomnias represent an example of "dissocitaion of sleep stages" with the overlaping of wakefulness and NREM sleep (confusional arousals, somnambulism and night terrors) or wake and REM sleep (REM sleep behavior disorder parasomnia). NREM parasomnias are a significant clinical problem that appears with functional reorganization of the brain as it transits throuh different states of consciousness. Aside from the above dissociation there are other physiological phenomena that render behavior more complex during sleep such as 1) activation of locomotor centers during sleep, 2) sleep intertia (confusion and desorientation during transition from sleep to wakefulness) and 3) instability of sleep stages (rapid oscilation(s) between seleep and wake).