I can relate to this, especially in the beginning of my therapy. It was very scary then and it happened often. Now, I am comfortable and know I can trust but it can still happen.
Fear sends us deep deep within. It is too frightening to listen, to think. It is protective to push it away.
I've told my therapist that it's as if she is speaking another language - sometimes one I do understand but cannot use to communicate verbally.
I used to say that when this happens, it is like the adults in a Charlie Brown animated program - where all you see are their legs and they all sound like "wah, wa-wah, wah, wah, wah, wah ...".