I'm not sure if it is exactly what you are experiencing, but something like this happens to me a lot. I just start to feel very removed from the situation that is going on around me, and sometimes it gets to a point where I will be listening to someone talk and then when they stop I will realize that I have absolutely no idea what they just said. It can feel like they are very far away somehow, or like there is some sort of barrier between them and me, if that makes sense.
I'll sometimes lose my train of thought while I'm talking too, have moments where I'm like "Wait, what the hell did I just say? For all I know I could have been speaking gibberish just now."
It's not all the time though; sometimes I am can be totally present, even sharp. It usually happens in concordance with other PTSD symptoms, and I do think it is disassociation related. A lot of times it happens when I start to think about traumatic memories, and my girlfriend can usually tell when it happens -- she'll often remark that I suddenly seem distant.
It does get to be pretty embarrassing and has caused a lot of problems for me at work. People find it exasperating if they know me, or if they don't then they just assume I am an idiot. Very frustrating.
Which I could offer some help, but best of luck and I hope it gets better for you.