Hey
I actually typed in google "shutting down in therapy" and your post was the first one on the list. I googled that as today my therapist let me in on what i do without realising, which is, shut down! It was fascinating as I was talking away then all sudden when inside got too painful *boom* was literally like a switch and I kind of froze and stared numbly to one side!
He said he will help me in bite size pieces to get it out as unhealthy to keep in but I also couldn't have a conversation about crying as again, he believes that goes against my internal permissions!
He is an amazing T and sounds like your one has really adapted to your needs too! Don't give yourself a bad time if you are as you are strong working through it and be patient with self