I tend to shut down in therapy, when things get hard. And my t always says, "where did u go?", or "what are u thinking?" One time, when I shut down completely, I apologized at the next session and told her that I had shut down and she just said, "I know u did." She obviously can tell when I dissociate, even if she doesn't make a big deal out of it. I didn't know that she knew until that day. So... I suggest asking your t if she notices. Because I bet she sees more than u think then that can get the conversation going