Thank you, myself (again!)

What you say makes sense, and yes, my T has discussed with me what are the triggers to me dissociating. It has only happened once in a session (though he did already know I had DID traits) so I guess it is early days yet. But we have talked about how I can keep myself in the here and now, and when he realises I am dissociating he is able to call me out of it by saying my name - that is enough.
Your description of the feelings when you start dissociating are similar to my own. I start feeling spaced out. I need to work hard at recognising what is going on and taking steps to deal with it. Because otherwise I do what you describe and floating off, being somewhen else and talking in that memory, ssaying how I felt then etc. We have talked a bit about the triggers - for me at the moment those are unclear largely, but talking about the incidents with the priest seemed to set it off in that T session, and feeling very upset is another trigger. There are people who remind me of my parents and that is another trigger.

We have talked about grounding techniques too - using my grounding stone, not focusing on blank walls but on somethign which is changing. All of that is still new but I see how I have developed strategies which enable my dissociation. Now I need to retrain them. I've been switching a lot (briefly) the last few days so this si something we need to discuss.
Thanks