theres a couple things in your post that jumps out at me...

a flashback is where a person has a past memory triggered to the extreme where it is like they are back in that day, time event..reliving it as if for the first time..

example one day I heard a car back fire. my mind brought to the surface the memory of when a clients abuser shot her in front of me. this was so vivid that I seemed to be back in the er and my client was getting shot. the noise of the hospital, the feeling of being in slow motion, the abuser, his statements and actions, my clients scream and actions, my yelling and actions......everything was so vivid it was like it was happening for real all over again. when this happened i was with my wife and it took her caring ways for me to realize I wasnt in the hospital er with a client.

what you posted reminds me of when I have what my treatment providers call an intrusive thought..sometimes I will be trying to fall asleep and I will start thinking about things unrelated to my going to sleep..

example last night while preparing to go to bed my thoughts of my routine was interupted with thoughts from new years. then when I was actually in bed instead of slowing down and going to sleep my mind kept thinking of unrelated to resting and sleeping thoughts, of being in the mine shafts. I ended up turning on the light to get to sleep so that I could open my eyes and remind myself that I was safe and not a child lost in the mine shafts after being abused.

so you see here where I live and work there is a definite distinction between what a flashback is and what an intrusive thought is.

I cant say whether what you experienced is a flashback or not. only you and your treatment providers can say whats a flashback where you are, and only your treatment providers can say how to tell when you are having a flashback, based on whats considered a flashback in your location and treatment providers definition of this.

one rule of thumb I use is go according to what ever your own treatment providers called it, if she said it was a flashback then it is and to find out how she knows it is one you will have to ask her how to tell when you have one.

here where I live and work getting stuck in a flashback means the flashback just keeps running and running over and over again with no let up. example my being stuck in the flashback that I mentioned above would be when that flashback ran its course it just loops on itself and continues again and again from the beginning over and over again. kind of like when I click on the "looping" button and play a favorite song over and over again on my computer, only in this case its a memory.

Again I cant say if thats what your own treatment provider means, only your treatment provider can say what she means by that phase.