Medical problems causing brain injury include aneurysm, brain tumours, subarachnoid haemorrhages and stroke. It also includes brain injury that may be sustained by alcohol and drug abuse.
Everyone is different in the way that they react to a brain injury.
Some may experience a period of unconsciousness lasting minutes, days or in some cases months. Others who suffer a mild concussion may not experience any loss of consciousness.
No one can be sure of the eventual outcome because the brain is so complicated. Recovery depends on a lot of things: for instance the severity of the injury and the 'knock on' effect of bruising inside the brain.
Most people with brain injury keep getting better slowly over many months, even years, but that could mean just getting better than they are now. Some people never recover to become exactly as they were before the accident.
It all depends on which parts of the brain were damaged and how badly.