When a person experiences a loss of consciousness, he or she is neither awake nor aware of the external environment. Loss of consciousness often is described as being "knocked out."

Attempts to arouse an unconscious person to an alert state may not be successful. The person may not respond at all or may respond with moans or nonpurposeful movements.

A loss of consciousness for longer than 60 seconds needs to be evaluated by a doctor.

Any loss of consciousness after a head injury, even if only for a short time, requires immediate evaluation by a doctor.