Prozac, perhaps? It was initially prescribed for my Generalized Anxiety Disorder, but it's helped in a lot of surprising ways -- things like flashbacks are far less frequent, with the intensity greatly reduced. They are still present, though mine were never severe in the first place -- but perhaps a higher dosage could work. The jump from 30mg to 40mg had the surprising effect of (almost) completely taking away my fear of having to be completely alone in the mountains, at night, in the pitch black dark -- a setting I regularly find myself in (horses).

I took valium before a dentist's appointment once (giant horse-sized needles were about to dig into the back of my mouth.... something no amount of novocaine could truly take care of) and spent the next 24 hours bothered by not. a. thing. in. the. world. It was an awesome 'vacation' from life, but I couldn't function on it in the longterm. I could see it working for intense flashbacks, though.. again, perhaps.