I feel for you big time.
I've only had the 'phasing out' as I call it a few times but it was scary as hell when I 'came to'.
For me, I'm still learning my triggers and what my therapist helped me with were 'Being Present' techniques have mainly worked when things are just starting - i.e when I get flickers on the edge of my vision or the voices are louder than normal or I'm feeling uneasy for no apparent reason.
However when I'm in one, rational thinking is out the window and 'Being present' is not a concept I can grasp as I don't know what's real and what's imaginary. I do know th