My brother was sitting at the computer and all of a sudden he blacked out. He said all he could remember was being in front of the computer then waking up to himself hitting his head on the wall. He has never had this happen to him before and he is not an alcoholic, so what could be the cause?
Blunt trauma to the head will work. I hit a metal pole with my head at high speed once and I blacked out.
It could be many different things. To be safe you might want to take him to a doctor. He could just be anemic or even narcoleptic or diabetic. He could also be taking a drug (legal or not, prescribed or not) that can be affecting how his body functions.
A doctor is your only safe bet to see what is wrong with him. If it happens again definitely make an appointment.