Mind went blank during therapy, couldn't think or speak?

We were talking about something I went through as a kid and discussing whether or not it could be considered trauma, and she started telling me ways I could combat the effects of it (in this case, the event(s) effected the way I act around my family and she said the solution was to try to act normally around my family). When she explained this, I started crying (I usually cry when we talk about it, so that wasn’t out of the ordinary), and I put my face in my hands and neither of us spoke for a minute or two, and I wanted to try to say something but I couldn’t, and then she asked me what was going through my head and I tried to think about what was going through my head but I couldn’t think of anything because my mind was completely blank; the only thing I could think about was what she was saying and I replayed it over and over in my head to try to get meaning out of it and come up with an answer but I couldn’t, and I decided to tell her I didn’t know what to say and I raised my head and opened my mouth but nothing came out and I started staring into space while she was asking more questions: “is this a panic attack?” – I shook my head (but I did start panicking at one point because I felt out of control because I couldn’t speak); “does this happen a lot? – I shook my head (this was the first time it had ever happened). Then I finally stuttered out “My mind is. Blank.” and she asked if I could stand up (I couldn’t), and she started asking me questions about my cats to help me get grounded, and I answered them until my mind was clearer and I could stand up and the session was over. I still have no idea what happened; help?