To me, it sounds like a type of dissociation. And yes, it is very common in abuse survivors who are talking about a traumatic event. Grounding techniques help. Does your t know about trauma work? Does your t offer these?

The first time it happened to me in session - when I tried to explain something about the first time I was abused, my t noticed straight away and brought me back by asking me to describe the trees out the window. She brought me back, told me that she could see how difficult it is for me to speak about and changed the topic so that I wasn't being retraumatised. We have slowly slowly approached the topic and I am able to articulate things better than at the beginning. I've been seeing my t for 3 years now and still haven't talked about the abuse in detail with her yet. That will come, as I need to talk about it to heal and rid the fear and shame.

Traumatic memories are stored differently than other memories. It is hard to talk about them as they are often stored in way where language is very difficult to connect with the traumatic events that occurred.

If you type in trauma and language you will find a number of articles etc. that explains this concept.