Unconsciousness is a state of unawareness (loss of consciousness) in which the person is unable to respond to people and other stimuli around him or her. Often, this is called a coma or being in a comatose state.

There are other changes in your level of awareness that can occur without becoming unconscious, or before becoming unconscious. Medically, these changes are collectively called "Altered Mental Status or Changed Mental Status." Such changes include sudden confusion, disorientation, or stupor.

Unconsciousness and any other SUDDEN change in mental status must be treated as a medical emergency.

If someone is awake but less alert than usual, an easy way to test for change in mental status is to ask a few simple questions -- What is your name? What is the date? How old are you? If the person doesn't know or answers incorrectly, then his or her mental status is diminished.

Being asleep is not the same thing as being unconscious. A sleeping person will respond to loud noises or gentle shaking -- an unconscious person will not.

An unconscious person cannot cough or clear his or her throat. This can lead to death if the airway becomes obstructed. Again, loss of consciousness or sudden change in level of consciousness must be treated as a medical emergency.

• Unconsciousness can be caused by virtually any major illness or injury, as well as substance abuse and alcohol use.
• Brief unconsciousness (or fainting) is often caused by dehydration, low blood sugar, or temporary low blood pressure. However, it can also be caused by serious cardiovascular or neurologic illness. Your doctor will determine if you need to be tested for such underlying disorders.
• Other causes of fainting include straining during a bowel movement, strenuous coughing, or hyperventilating.