Ans. is 'b' i.e., Nightmares Important events occuring during sleepA) Deep sleep/slow wave sleep disorder : - These events occur during stage 3 & 4 of NREM. Important disorders are: -i) Somnambulism (Night walking): - Patient walks during sleep.ii) Sleep terror or night terrors (pavor nocturnus): - The patient suddenly gets up screaming, with autonomic arousal (tachycardia, sweating). Sleep terrors are rarely remembered in the morning (in contrast to night mares). No treatment is required only reassurance is required. However, in severe cases benzodiazepine can be used.iii) Sleep-related enuresis (Nocturnal enuresis/bed wetting): - Repetitive voiding occurs during sleep. First line of treatment is behaviour therapy. If behavioral therapy fails, desmopressin (DOC) and Imipraminecan be used.iv) Bruxism (Teeth grinding)v) Sleep-talking (Somniloquy).B) REM sleep eventsi) Nocturnal penile tumescence: - It is spontaneous occurence of an erection of the penis during sleep. It is a normal phenomenon and occurs for 80-120 minutes per night. Nocturnal penile tumescence can be used to differentiate between psychogenic impotence and organic impotence as nocturnal penile tumescence is preserved in psychogenic impotence but not in organic cause of impotence.ii) Night mares (dream anxiety disorder): - They are characterized by fearful dreams occuring in the last one third of night sleep. The person wakes up frightned and remembers the dream vividly (in contrast to night terror).iii) Narcolepsy: - This is characterized by excessive day time sleep, often disturbed night time sleep and decreased in the REM sleep. Age of onset is between 10-20 years. There is irresistable desire to sleep and bouts of sudden sleep each lasting for 10-30 minutes occuring during day time. In majority of cases narcolepsy is associated with one or more accessory symptoms: -a) Cataplexy: - It is the most common accessory symptom and is characterized by sudden decrease in muscle tone either, local or generalized.b) Hypnagogic hallucination: - Hallucination occuring just before falling asleep. When hallucination occurs just before awakening it is called hyponopompic hallucinations.c) Sleep paralysis (least common)