I got into a similar spot a few weeks ago. the silence grew longer and heavier and made things so much worse. Finally I managed to get out, "well, you're going to have to say something, because I can't." T2 immediately started talking to me.

Yalom says in therapy we should "strike while the iron is cold". So at the next appointment, before we got into anything hard, I told her what it made me feel like, knowing I was shutting down & her just sitting there, and I told her what I need from her if I start to go away (I do not list specifics, my needs may be different from yours).
She thanked me for letting her know what I need, & the next time the same sort of situation came up again, she acted on what I had told her, and it helped so much - made me aware that the other person in that room was really someone on my side, someone who was actively trying to help me.

I don't know if this is helpful, but thought I would mention it.