Sounds like you did some damage to your brain from running into the wall! This could have been fatal, obviously, so I'm glad you're mostly okay. Are you in a country where you have access to healthcare? I think it would be a good idea for you to see a doctor even now, to see if you can get some answers about what happened, maybe with a CT scan or something like that. Something about the way you write makes me think you're British. If so, you may also be able to get free speech therapy on the NHS. The therapists in hospitals have experience in working with this type of stuttering.