Emotions and Fitness

I am not sure if this is the right category to post it, but here goes.

Last year, I started going to the gym and I was super excited, totally motivated and I felt happy and great. Then, out of no where, I went to a spin class, like usual and just broke down crying on the bike. After class, the instructor brought me into the office and showed me pictures of herself a year ago to show how far she, herself, had come. She had lost over 120 pounds. We talked and talked about a lot of things.
I don't know what caused me to break down. I wasn't even thinking about anything. I was not CONSCIOUSLY thinking about anything that would have depressed me. I had done spin class several times before without incident. I wasn't having any CONSCIOUS thoughts of " I can't do this" or "what have I done to myself" I was not PMS'ing. It took a few days, but I picked myself up and I was fine.

Last week, after several months of not dieting or working out, etc, I went back to the gym and was doing a step class, doing fine, and the same emotions came over me. This time, I stopped myself before I broke down, finished the class and when I got in my car, totally broke down in sobs. I really don't understand it.

I don't feel this when it comes to food, it is only with exercise. Has anyone had a similar experience?