For many brain injury survivors they have no recollection of the incident in which they sustained their injury.
They often have to piece it together from what people have told them or what they think might have happened, others are simply happy not knowing many details.
Brain injury survivor David Wheeler found out what happened to him after a nightmare woke him from his sleep and his mother noticed him distressed.
He said: “When I woke up, my pillow was quite wet and the sheets were all over the bed. The nightmare was terrifying, I have never had one like it. All I could see was what seemed to be the wreckage of my motorbike, under this massive black object.
“I was on the floor screaming and there were parts of my motorbike all over the road and my body was just protruding from this large object
"I remember trying to put it all to the back of my mind and went downstairs to talk to my parents.”
When David’s mother saw him, she knew something was troubling him.
David said: "She asked me if I was OK and I told her I was. I kept the motorbike dream to myself because she was always worried about me riding it.
"But she kept pushing to find out what was wrong and I ended up telling her what I’d dreamt. What she said next, will stay with me forever.
“She said ‘David, you have had a motorbike accident`. I remember feeling bewildered and confused. I told her that I hadn’t, she replied that I should stop being silly and walked away.”
David said his mind was whirling trying to understand what was going on and he asked his mother again for answers.
He said: “I asked her again what she had meant and then she said ‘Think very carefully, how you answer this next question. Now, David are you telling me you don`t remember your accident, or being in hospital?.' I shouted `What accident?!'."
It was at this point that David’s mother realised what was happening and she asked him to look in the mirror.
David, who was eighteen at the time, said when he looked into the mirror he knew his life would never be the same again.
He said: “The hair on the left side of my head was getting a bit long but the hair on the right side of my head had all been shaved off. All I could see was a very large Y shaped scar and in the centre was a dent in the shape of a circle, the size of a fifty pence coin.”
“That`s how I found out about my accident. I have no memory of being in hospital at all.”
David had sustained a traumatic brain injury when a double-decker bus full of school children knocked him off his motorbike in 1979.
The wheel of the bus went over his head and pinned him between the top of the wheel-arch. This impact forced the top of his spine into his skull causing the brain injury, he was in a coma for three weeks.
Now 40 years later he lives with the lasting effects of the accident, including severe memory problems, epilepsy and balance issues. But he still manages to get around using a mobility scooter and after some very dark days he says he now has a positive perspective on life.
He said: “Sadly both my mum and dad have passed away and although I have a brother, we don`t speak to each other. I now live in a sheltered housing complex in Swansea and I am so happy living here.
“All my worries that I had after my accident have gone and I go to a private art teacher who is marvellous with me. I also go to a group for people with memory problems called `Forget me nots`. It’s very nice.
“I have learnt over the years that not knowing what the future holds can and does worry people. But life is what we make of it!
Even though I have no family or real friends I`m glad when I wake up. I see the sun shining, and I think to myself, I might take the scooter out for a run today.