I think the classification of brain injuries can be very misleading to people. Many times you'll hear something classified as a mild, moderate or a severe brain injury. And, I think we think of that as having some relationship to the damage done to the brain. What these labels actually identify is how long the person was unconscious. And, remember that most brain injuries do not result in a loss of consciousness at all.
Many people will have this feeling of being dazed, stunned or kind of foggy. While they are not unconscious this is classic evidence of a brain injury. But someone who has a mild brain injury, for instance, what they are talking about is a brief period of loss of consciousness. Someone with a moderate brain injury would have a longer period of loss of consciousness, typically less than 30 minutes. And, someone who has a severe brain injury has a much longer loss of consciousness.
This identification of a traumatic brain injury is not a reflection of the damage done to the brain. All brain injuries cause injury or damage. And, all brain injuries are likewise serious. Keep this in mind when you hear these terms, mild, moderate and severe.