**Question:** Night mares are seen in

A. Delirium
B. Psychosis
C. Somnambulism
D. Narcolepsy

**Correct Answer:** D. Narcolepsy

**Core Concept:** Narcolepsy is a chronic neurological disorder characterized by excessive daytime sleepiness, sudden urges to sleep, and cataplexy (temporary muscle weakness during waking hours). It is caused by a deficiency in hypocretin (orexin), a neurotransmitter produced in the hypothalamus.

**Why the Correct Answer is Right:** Narcolepsy directly relates to the question of night mares, also known as hypnagogic hallucinations, which are vivid, sensory experiences occurring during the transition from wakefulness to sleep. In narcolepsy, the deficiency of hypocretin leads to disrupted sleep architecture and reduced brain function, causing these night mares.

**Why Each Wrong Option is Incorrect:**

A. Delirium: While delirium can present with sleep disturbances, it is a temporary condition usually caused by an underlying medical illness, injury, or substance use. Night mares are not a defining feature of delirium.

B. Psychosis: Psychosis is a mental disorder characterized by hallucinations and delusions, not specifically related to sleep disturbances or night mares.

C. Somnambulism: Somnambulism, also known as sleepwalking, is a sleep disorder characterized by walking or engaging in other activities during sleep. It is different from night mares, which occur during the transition to sleep.

**Clinical Pearl:** Narcolepsy is a crucial concept in understanding sleep disorders and their implications on sleep-related phenomena like night mares. These hallucinations can cause distress and negatively impact sleep quality, which is why proper diagnosis and management of narcolepsy are essential for patients suffering from these symptoms.