I know how you feel Apt. I had that happen 2 weeks ago. All was good and productive until the end when I hit a flashback for the first time in years, and completely zoned out on what my T was trying to say. I regained myself and was fine, but it left me scared for the next appt. The next appt was nice though, I told her about it and she was very comforting and understanding.
I understand the fear. I understand the over analyzing, the obsessing, the worrying. I'm there, I've been there, I'm still going to be there for a while. Feel free to PM me if you need a shoulder to lean on, or an ear to rant to. You've helped me, I'd be more than happy to try and help you as well if I could.