I was going to say what Skies mentioned. Trauma means many different things to people and we often associate the word with something big and destructive. I think that "checking out" can be a healthy reaction to overwhelm in the moment and does not necessarily need to have roots in the past. Just an emotional reaction to something that feels too much to process in the moment.

I don't tend to have memory blanks per se that I know of about my therapy sessions but often have delayed emotional reactions in many situations, not specific to therapy. It often serves me well because I can focus on a task at hand, or a crisis situation that needs to be resolved, without freezing or collapsing. But when I try to recall what I was feeling, it seems a bit like a blur. I also have similar memories about fragments of my childhood: remember events clearly but not so much the emotional content. What's interesting is when later some unexpected event or stimulus taps into these things and pull stuff out of my unconscious memories suddenly, eg. hearing a piece of music that reminds me of seemingly forgotten stuff.

As mentioned earlier, anxiety can cause states that feel dissociated... eg. the concept of depersonalization/derealization. I sometimes feel that way, not in therapy, but in situations I am highly anxious about. It can be quite annoying because I can hear people asking me questions and telling me something but it's as though I am unable to process or comprehend it in that very moment.