I do this loads, too. Exploring with T why I blank out or freeze up has really helped. I still do it, but I am getting a tiny bit less mad at myself for doing it! Getting frustrated with myself tends to intensify the blankness, anyhow.

I encourage you to be brave and bring this up with your T! Remember, you don't have to (and won't) figure out why or how to change it all in one session. But bringing it up as a concern of yours is the first step in taking control of it.