Thank you all so much for your kind and helpful words. I didn't expect to come back after class the next morning and find so many replies!
Since I left the practica so early, drove to the class location and had a bunch of time, I walked around and tried to calm down. As I said, I think, I completely got over the teary part, but what was more disturbing was how my stomach absolutely flared up. Which had never happened to me, so now I have to look into this, otherwise I will have serious issues whenever I'm in any stressful situation. (My mom was prone to ulcers....I never had that problem before.) The stomach thing lingered on into the first 30-40 minutes of the class and was pretty intense, though I kept a good front. I couldn't eat any food (didn't want any) and it was hard to pay attention to what they were doing.
Only Marsha was there from the practica. Otherwise about six other students, most of whom I knew, and the teachers. She asked me why I'd left and I just said my stomach had acted up, but was better now.
It turned out to be a great class, but it was so hard for me to stay in the moment and not get into "monkey mind" about what had happened, which should no longer have mattered. I am not the best mindfulness student! It took a while, but things simmered down internally. I had a few great dances with one of the instructors, Paul, who was really happy to see overall progress I'd made. (I take private lessons also with his co-instructor, so she is much more on top of how I'm progressing.)
By the end of the evening I was feeling about 70% back to normal.
I may take another private lesson today or tomorrow and speak to my female instructor about this. Actually I will probably have to, since it's an expectation that we all go to practica as a supplementary means of practicing what we do in class. She can hear me out and offer some advice, or at least get the heads-up. It's not an unusual situation at all...it's extremely common.
In fact I got an email this morning from one of my woman friends who had been there and was feeling bad that I had left while she was out on the floor. She and I dance at least once or twice together each week (she's learning how to lead, precisely because this is one way women can get some more control over their situation and not need to passively wait). She was apologizing to me, clearly understood what had happened, and now I feel pained to see the cascading effect. It will sadden her a lot if I stop going to that event.
It is a good thing in life to have a thick skin. I need mine thicker.
Thanks again. I think bringing this up for discussion with my teacher will be a good thing.