Even slight bleeding in or on the brain leaves a clot which can take years to be absorbed.
I had a wreck on my bike when I was 11 and it was 22 years before I had normal results on an EEG.
Am waiting on the expert witness re head injuries to testify. Can’t have a head injury bad enough to open up the gashes in his head and not have some internal injury too.
IIRC the law says to defend yourself against death or body injury. Seems to me the injury has been done.