Have you tried upper cervical chiropractic treatment?
Hitting the way he did it very well could have misaligned his c1 c2 vertebra.
more info
www.upcspine.com
Sign / Symptom Checklist
http://www.upcspine.com/self.htm

http://www.google.com/url?sa=t&rct=j...78597519,d.cGU

various videos about it
http://www.youtube.com/watch?v=0N5lU1oJF6Y