Anxious arousals originate from all sleep stages and can be classified as: a) stage 4 night terrors; b) rapid eye movement (REM) nightmares; c) stage 2 awakenings; and d) hypnagogic nightmares. We have confirmed Broughton's finding that the night terror, the most severe type of episode, does not occur in sleep but as part of the “arousal response,” a complex of autonomic discharge and behavioral symptoms. The full blown night terror is a fight-flight episode combining sleep utterances, sleep walking and hallucinated or delusional mental content associated with terror.There is a significant positive correlation between intensity of night terror and the amount of delta sleep preceding arousal,e.g.,stage 4 arousals designated as night terrors are preceded by longer periods of stage 4 than arousals of lesser intensity (p<.05). About two-thirds of both stage 4 and night terrors occurs in the first non-REM (NREM) period. The night terror arises out of physiologically quiescent sleep as indicated by the normal or slightly less them normal cardiorespiratory rates during the first NREM period and absence of skin resistance changes prior to the attack.The night terror is ushered in by sudden loud piercing screams, the subject passing into an aroused state characterized by alpha rhythm, motility, often somnambulism, intense autonomic discharge (precipitous doubling or even tripling of heart rate, great increase in respiratory amplitude, marked decrease in skin resistance), brief duration (1 to 3 minutes), varying degrees of amnesia for the episode, and rapid return to sleep. The night terror is a much more severe phenomenon than the REM nightmare although the latter is far more frequent. The nightmare occursin REM sleep,is characterized by slight autonomic fluctuations, compared to the night terror, and, in half of instances, a “desomatization” of the anxiety response, that is, absence of its physiological concomitants. The REM state is physiologically activated to begin with, constituting a preparation for fright, possibly a buffer against the extreme terror of the stage 4 variety.The important problem of the triggering mechanisms of the night terror remains unsolved: whether the attack is precipitated by ongoing mental content during delta sleep, or represents a psychosomatic “arousal response“ (Broughton). The fact that it can be induced artificially by sounding a buzzer speaks in favor of the latter, the finding of significant mental content in favor of the former. The night terror is not a dream but a symptom emerging from stage 3-4 sleep, associated with a rift in the ego's capacity to control anxiety.