Hypersomnolence is characterized by excessive daytime sleepiness, with a tendency to fall asleep at inappropriate times and places, for example during meals, telephone conversations, at the wheel of a car.
Causes of hypersomnolence include:

Narcolepsy or the narcoleptic syndrome: may be accompanied by other features such as sleep paralysis, hypnagogic hallucinations, cataplexy
Midbrain lesions
Idiopathic CNS hypersomnia Kleine-Levin syndrome
Nocturnal hypoventilation, due to:
Obstructive sleep apnea-hypopnea syndrome (OSAHS; Pickwickian syndrome)
Chest wall anomalies
Neuromuscular and myopathic disorders affecting the respiratory muscles, especially the diaphragm, for example:
Motor neurone disease Myotonic dystrophy
Metabolic myopathies, for example, acid maltase deficiency Mitochondrial disorders
Drugs: benzodiazepines, ergot-derivative dopamine agonists Post-stroke sleep-related disorders.

Nocturnal hypoventilation as a consequence of obstructed breathing, often manifest as snoring, causes arterial oxygen desaturation as a consequence of hypopnea/apnea which may lead to disturbed sleep, repeated arousals associated with tachycardia and hypertension. Clinical signs may include a bounding hyperdynamic circulation and sometimes papilledema, as well as features of any underlying neuromuscular disease. OSAHS may present in the neurology clinics with loss of consciousness (sleep secondary to hypersomnolence), stroke, morning headaches, and cognitive impairment (slowing). Investigations may reveal a raised hematocrit and early morning hypoxia. Sleep studies confirm nocturnal hypoventilation with dips in arterial oxygen saturation. Treatment is with nocturnal intermittent positive pressure ventilation. Modafinil is also licensed for this indication.


Cross References

Asterixis; Cataplexy; Papilledema; Paradoxical breathing; Snoring