After acute severe brain damage, many people are rendered unconscious or comatose for more than 24 hours. Although a significant number can still recover fully, some will not and a substantial minority remain unconscious for days, weeks or longer. These patients have a prolonged disorder of consciousness. If recovery of awareness has not occurred by six months after hypoxic or hypoglycaemic brain damage and 12 months after most other causes of brain damage, then the patient is very unlikely to recover any awareness and is described as being in a permanent vegetative state.