Decreased consciousness is reduced alertness or awareness.

Stuporous; Mental status - decreased; Loss of alertness; Decreased consciousness; Alertness - decreased; Changes in consciousness; Obtundation; Coma; Unresponsiveness

A persistent coma is called vegetative state.

Many conditions can cause decreased consciousness, including:

• Alcohol intoxication
• Drug intoxication (particularly opiates, narcotics, sedatives, and anti-anxiety or seizure medications)
• Arrhythmia
• Brain disorders
• Central nervous system diseases
• Lack of oxygen (hypoxia)
• Abnormal blood sugars (diabetic coma)
• Electrolyte or mineral imbalance
• Exposure to heavy metals or hydrocarbons
• Extreme fatigue or sleep deprivation
• Ketoacidosis
• Head trauma
• Heart failure
• Hypoglycemia (low blood sugar)
• Increased carbon dioxide levels (hypercarbia) often seen in emphysema
• Infection
• Low blood pressure (hypotension)
• Metabolic disorders
• Thyroid or adrenal gland disorders
• Seizures such as those related to epilepsy
• Shock
• Stroke

Blok BK, Newman TM. Syncope. In: Tintinalli JE, Kelen GD, Stapczynski JS, Ma OJ, Cline DM, eds. Emergency Medicine: A Comprehensive Study Guide. 6th ed. New York, NY: McGraw-Hill; 2004:chap 52.

Huff JS. Altered mental status and coma. In: Tintinalli JE, Kelen GD, Stapczynski JS, Ma OJ, Cline DM, eds. Emergency Medicine: A Comprehensive Study Guide. 6th ed. New York, NY: McGraw-Hill; 2004:chap 259.

Kirsch TD. Head injury. In: Tintinalli JE, Kelen GD, Stapczynski JS, Ma OJ, Cline DM, eds. Emergency Medicine: A Comprehensive Study Guide. 6th ed. New York, NY: McGraw-Hill; 2004:chap 255.