A person who is in a coma is in a deep state of unconsciousness where he or she cannot be woken and does not respond to outside stimulation. There are many potential causes of a coma, including head injury, extreme changes in blood sugar (very high or very low), or excessive intoxication. A coma is a medical emergency that requires immediate care in order to help preserve and protect brain and body function.

A coma may last several days or weeks, though the majority of people begin to wake in under 2 to 4 weeks. There is the potential for lasting intellectual, psychological, and physical impairments following a coma, depending on the extent of damage done to the tissues of the brain. The longer the coma lasts, the more likely it is that the individual will enter a persistent vegetative state.

Causes
Damage to the brain can result in a coma. There are many potential causes of this kind of damage or injury, including:
-- traumatic brain injury, such as from a car accident or fall
-- Apoplexy (stroke)
-- tumor
-- repeated seizures
-- infection or swelling in the brain, such as from meningitis or encephalitis
-- anoxic brain damage (insufficient oxygen supply to the brain), such as from a heart attack
-- Hyperglycemia (very blood sugar) or Hypoglycemia (very low blood sugar), such as from uncontrolled diabetes
-- excessive exposure to toxins, alcohol, or drugs

Symptoms
Individuals who are in a coma have minimal brain activity and cannot be woken. This means that although they may display behaviors such as opening the eyes or making noises, they are unaware of the environment around them and the behaviors are not intentional. Common symptoms of a coma include closed eyes, inability to wake, reduced brainstem responses (such as the pupils not dilating when exposed to light), and reflex-only movements even in response to painful stimuli such as sternal rubbing.