Then what you do is go back to your doctor and say "The lithium doesn't seem to be working, can we try something else?" Your doc will have suggestions and solutions. If he doesn't do it on his own, ask to be referred for a psychiatric consultation. Youll get a full psych work up done on you with a psychiatrist and then you can begin to work on what's brought this on, if it has anything to do with the accident, etc. You may feel guilt, shame, horrified, scared, or traumatized, but how would you expect to feel after seeing something like that?
I mean c'mon, you think there is an actual disorder called Gulf War Syndrome? Just cause you were in the Gulf War doesn't give you a brain disorder. What HAPPENED in the war can cause you to have feelings and thoughts that you need to seek help for, but can we call that a mental disorder? No? Those are normal thoughts and feelings.
To watch someone die and NOT be affected by it, now THAT is a mental condition.