The thing I would add to what Jun listed is that even in a "minor" head injury, some of the symptoms may persist for quite a while. It is reassuring, if 4 or 6 months after you have had a concussion, you are having mood swings or headaches, that there is a REAL organic reason for it; you are not having a psychological problem.
For anybody having ongoing long term symptoms (migraines, cognitive changes) there is ongoing research with biofeedback and brainwaves that is showing good results, and I encourage you to search locally for a practitioner/researcher. (BTW, I am NOT involved with or affiliated with any of these folks. I was at one time an acute rehab RN, and my husband had a severe concussion many yrs ago.) Links