First PTSD hello!
When I have flashbacks, I have learned to repeat that this is a flashback and it's 2011 and the month is July and just talk out loud if you can so your whole being can feel and hear what your asking your body to do in a way.
I say, this is ONLY a Flashback and I try to write down the basic part of the flashback. Then if I don't know what triggered me into having a flashback, I write down everything I could remember before I had this flashback. Oh also like I have already beat this and this is only a memory. Minimize it until you can get ahold of the memory. Then when your with your T, talk it out with your T and even maybe draw it out but I wouldn't do that until I know without a doubt I won't retrigger myself.
I hopes this helps and if you need to chat, pm me and I don't mind listening....

Crew