It's a form of PTSD--you may be re-experiencing the past via memories. The close relationship of some psychodynamic therapies trigger such memories.

You probably can't describe it because these experiences happened before you could talk (pre-verbal). For me, it always felt like impending death.

I have the same issue-it happened to me over and over again in the first year of therapy and much of the 2nd year. Your T can help you by not reacting as your parents once did. Lots of reassurance and attentiveness helps.

Hope you email her.

Thought provoking question.