I get suddenly shut down, too. T and I have been struggling with how to deal with it for years. He keeps reframing it in different ways to try to understand why it happens.

What has helped me is talking about being stuck, when it happens, and how it frustrates and scares me, etc. I used to just seethe and try to force myself to talk about what I'd been saying earlier but that just kept me shut down. When I talk with T about how being shut down feels, I am at least still connecting with him and it helps.