Decreased consciousness may result from a multitude of conditions including intoxication (drug, alcohol, or toxin), metabolic abnormalities, seizure activity (epilepsy), central nervous system diseases and conditions, head trauma, shock, decreased oxygen (hypoxia), and decreased blood pressure (hypotension).

Decrease in consciousness, unconsciousness, and coma almost always require medical evaluation (with the possible exception of alcohol intoxication, simple fainting, or a previously recognized seizure disorder).

Persistent coma is called vegetative state.

• head trauma
• extreme fatigue or sleep deprivation
• seizure activity
• stroke (CVA)
• heart failure
• arrhythmia
• diabetic coma (diabetic hyperglycemic hyperosmolar coma)
• hypoglycemia
• ketoacidosis
• head injury
• drug intoxication (for example, from analgesics, anticonvulsants, antihistamines, benzodiazepines, digoxin, ethanol (see ethanol overdose), heavy metals, hydrocarbons, barbiturates, insulin, lithium, organophosphates, phencyclidine, phenothiazines-oral, salicylates - oral, or tricyclic antidepressants)
• electrolyte abnormality (hypernatremia, hypercalcemia)
• infection