The outlook depends on the extent of the brain injury. This is determined by how long the brain lacked oxygen, and whether nutrition to the brain was also affected.
If the brain lacked oxygen for only a very brief period of time, a coma may be reversible and the person may have a full or partial return of function. Some people recover many functions, but have abnormal movements, such as twitching or jerking, called myoclonus. Seizures may sometimes occur, and may be continuous (status epilepticus).
Most people who make a full recovery were only briefly unconscious. The longer a person is unconscious, the higher the risk for death or brain death, and the lower the chances of recovery.