Really, as a (trauma?) T, he should know about the delayed reactions to triggers and what's behind this delay. It's not as if you choose to hold back...

For me it's some form of dissociated state. And only later, when I'm by myself, it hits me full force. For some reason in my past it was paramount that I don't let on about what is really happening inside of me. So the safest way to do this was not knowing myself what's going on. Interrupting contact with myself.

Part of the healing process (for me) seems to be that re-gaining contact with myself comes with stages of immense inner pain and turmoil. And fear and panic, and whatelse. And there might be some truth in your guess from your first post (grounding exercises interrupting dissociation) - your 'normal' coping-strategy is put out of order, but you haven't found an adequate alternative coping mechanism yet. Because it takes time and such...

Maybe knowing that this dark hole might be some sort of delayed reaction to some actual trigger might help? I sometimes visualize this reaction like a giant pendulum. There will be a turning point and the pendulum will swing back again, and eventually losing it's massive momentum.

Hugs, c_r