Is the passing out due to high pain levels - or is there some other possible cause for it?

Head hitting things - can cause the c1 & c2 to get out of alignment which can start up various troubles. {called Upper cervical/ atlas/axis}

some info links-
Chiropractic care info- a good one can help with many symptoms:
http://www.upcspine.com/self.htm
http://www.uppercervical.org/subpag...b/about_faq.php
http://www.spineuniverse.com/index.html
http://www.coloradochiropractic.org/.../glossary.html