Some of this may be PTSD. My therapist (very good TBI-aware psychologist) says that PTSD is common among people who have had head injuries, car accidents, etc. and that recovery often takes at least a couple of years. I had horrible nightmares and insomnia early in my recovery, along with a few choice panic attacks. I'm doing a lot better overall, although I still deal with these symptoms to some extent (the panic attacks appear to have stopped altogether). I'm almost a year and a half post-injury.

My therapist also recommends doing a particular relaxation exercise daily (she gave me a handy cassette for this, about 35-40 mins) and being disciplined about maintaining good sleep habits. The goal is to train yourself to relax more readily and generally keep stress levels down.