Trauma is never an easy thing to deal with, especially if it's the first time you've seen something like that.
Very early on in my aeromed career, we attended an accident which involved a girl in her late teens that'd been involved in a car accident. Despite the best efforts of all medical crews, she couldn't be saved, and died there on our stretcher. That was hard to deal with, but I think the hardest part was actually seeing her distraught father having to deal with her death, without any family there with him.
Took probably a good 6 months to deal with that, then another 6 before I no longer really think about it anymore, and trauma's since don't seem to bother me much (the constant exposure deals with that).
My advice would be to at least sit down with someone else who is either a professional in the counselling field, or perhaps even someone from the emergency crew who attended the accident you saw. Then at least they're on the same page when it comes to what you've seen. Sometimes talking to someone who also saw it, helps you unload a bit more about what went on.
Post traumatic stress though is a very real issue. Don't bottle it up inside of you.
Cheers
morno