I agree with Echoes, coconut.... talking about the shutting down IS really important.

If I am unable to talk about specific abuse stuff, T and I talk about not being able to talk about it - WHY am I shutting down? What am I scared of? What does it feel like? THOSE have been my most healing sessions, for sure. You can talk about the "here and now" and the feelings you are having in session, and it can be safe, even though it feels really scary.