(I) Cataplexy and narcolepsy: Narcolepsy is characterized by excessive daytime sleepiness, often with episodes of irresistible sleepiness, along with sudden muscle weakness (cataplexy). Cataplexy may be triggered by strong emotions or surprise. Symptoms include narcoleptic sleep attacks, cataplexy, sleep paralysis, hypnagogic hallucinations (at the beginning of sleep), hypnopompic hallucinations (upon awakening), disturbed night sleep, and automatic behavior. Onset is most often in adolescence. Sleep attacks can occur in inappropriate situations (for example, while talking, walking, or sitting) and typically last about 30 minutes. This can impair school and work performance.
Cataplexy is a sudden loss of tone in voluntary muscles, triggered by emotions such as anger, rage, or laughter, with complete return of consciousness within seconds to minutes. Secondary causes of narcolepsy-cataplexy include strokes, encephalitis, midbrain tumors, and cerebral trauma.
(II) Idiopathic hypersomnia: This condition presents with excessive daytime sleepiness and either normal or prolonged nighttime sleep. Sleep is not refreshing. There is no history of snoring, cataplexy, or nighttime awakenings.
(III) Insomnia: Insomnia is the most common sleep disorder. Patients present with difficulty initiating sleep and maintaining sleep. Early morning awakening, excessive daytime sleepiness, and functional impairment may occur. Symptoms occur more than 3-4 times per week for more than a month. Primary insomnia is idiopathic. Secondary insomnia may be due to acute stress, alcohol or drug abuse, psychiatric disorders, and other causes.
(IV) Circadian rhythm sleep-wake disorder: These disorders are caused by disturbances in the body clock and sleep-wake cycle. Common causes include jet lag, night shifts, and diseases such as Alzheimer’s and Parkinson’s disease, as well as head trauma or encephalitis. They can cause insomnia, excessive sleepiness, malaise, irritability, depression, and an increased risk of cardiovascular and metabolic disorders.
(V) Primary sleep terror disorder and nightmares: Sleep terrors occur during NREM sleep and are seen in young children aged 5-7 years. They are characterized by sudden arousal from sleep with intense fear, screaming or crying, autonomic manifestations (such as tachycardia, tachypnea, and sweating), and amnesia for the event on waking. They are often precipitated by sleep deprivation, fatigue, and sedative-hypnotics. Sleepwalking is sometimes associated.
Nightmares occur during REM sleep and are commonly seen in children. They are characterized by frightening dreams followed by awakening from sleep with vivid memory of the event. They can be precipitated by medications such as antiparkinsonian drugs, beta blockers, and anticholinergics.
(VI) Sleepwalking or somnambulism: Sleepwalking occurs during slow wave sleep. It is more common in children aged 5-12 years, but it can also be seen in adults. Motor activity may include walking around the house, driving, eating, or (rarely) acts of violence. There is no memory of the event. Sleep deprivation often precipitates sleepwalking.
(VI) REM sleep behavior disorder: This disorder is seen in elderly individuals and occurs during REM sleep. It is characterized by abnormal motor activity during sleep, such as acting out dreams or violent behavior. It is more common in neurodegenerative disorders such as Parkinson’s disease, Lewy body dementia, and supranuclear palsy. It may also be caused by drugs such as SSRIs, TCAs, and anticholinergics, and by alcohol. Reduced presynaptic dopamine transporter and postsynaptic D2 receptors have been found in this disorder.
(VII) Restless legs syndrome or RLS: RLS is characterized by an unpleasant “creeping” sensation, often felt as originating in the lower legs, and it may be associated with aches and pains throughout the legs. This sensation often causes difficulty initiating sleep and is relieved by movement of the legs (for example, walking or kicking). Abnormalities in the neurotransmitter dopamine have often been associated with RLS.
(VIII) Obstructive sleep apnea: Obstructive sleep apnea is characterized by recurrent episodes of upper airway collapse during sleep, resulting in airway obstruction and apnea-hypopnea. It is more common in obese, middle-aged males and in postmenopausal females. It presents with snoring, daytime sleepiness, choking, shaking or jerking during sleep, and daytime sleep attacks when the individual is relaxing. It may lead to hypertension, polycythemia, cardiac arrhythmias, metabolic syndrome, impotence, headaches, and heart failure.
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