I was reading recently that having nightmares after car accidents like yours is a good thing; you mind is telling you your feelings are "right"; it IS scary to have had your accident.

Were I you I'd be "glad" and thank your dream/nightmare for confirming your feelings and sort of "accept" the nightmare and maybe you wouldn't need it anymore? Did you talk to anyone about your accident after it happened, work it through? Your insides are just trying to balance you, have to stay in balance and do whatever is necessary to get that way. If you have conscious trouble working on your experiences, your brain will compensate and you'll get nightmares to help support you. It's a good thing, even though it isn't fun (like taking bitter medicine).