Somnolence (or "drowsiness") is a state of near-sleep, a strong desire for sleep, or sleeping for unusually long periods (c.f. hypersomnia). It has two distinct meanings, referring both to the usual state preceding falling asleep, and the chronic condition referring to being in that state independent of a circadian rhythm. The disorder characterized by the latter condition is most commonly associated with users of prescription hypnotics, such as mirtazapine or zolpidem.

It is considered a lesser impairment of consciousness than stupor or coma.

Hazards

Sleepiness can be dangerous when performing tasks that require constant concentration, such as driving a vehicle. When a person is sufficiently fatigued, he or she may experience microsleeps.

Associated conditions

• advanced sleep phase syndrome
• atypical depression
• bruxism
• brain edema
• cerebral hypoxia
• clinical depression, especially seasonal affective disorder (SAD)
• delayed sleep phase syndrome
• dysautonomia
• encephalitis - (viral, bacterial or other agents)
• hydrocephalus
• hypothermia
• hypothyroidism
• infectious mononucleosis (glandular fever)
• intracranial hemorrhage such as due to ruptured aneurysm
• increased intracranial pressure; for example, due to brain tumors
• Lyme disease (borreliosis)
• medications
• analgesics - mostly prescribed or illicit opiates such as Oxycontin or heroin
• anticonvulsants / antiepileptics - such as phenytoin (Dilantin), carbamazepine (Tegretol), lamotrigine (Lamictal), Lyrica (pregbalin)
• antidepressants - for instance, sertraline and venlafaxine
• antihistamines - for instance, diphenhydramine (Benadryl)
• antipsychotics - for example, thioridazine, quetiapine, and olanzapine (Zyprexa), but not haloperidol
• dopamine agonists used in the treatment of Parkinson's disease, e.g. pergolide and ropinirole
• HIV medications - for example, Sustiva and medications containing efavirenz
• hypertension medications - such as Norvasc
• tranquilizers / hypnotics - especially benzodiazepines, such as temazepam (Restoril) or nitrazepam (Mogadon), and barbiturates, such as amobarbital (Amytal) or secobarbital (Seconal)
• other agents impacting the central nervous system, in sufficient or toxic doses
• myelofibrosis with myeloid metaplasia
• narcolepsy
• Paget's disease
• sleep apnea
• sleep deprivation / insomnia
• starvation
• stroke
• traumatic brain injury

See also

• Insomnia
• Hypersomnia
• Dyssomnia
• Fatigue (physical)