So yesterday at the gym, I was doing crunches with 190lb weight on my back/arms. (It was a machine, not free weights.) When I was done with my 3rd set of 20, I got up and my left side of the bottom of my stomache got really hard and swelled out immediately. The pain was emense. Then, it went back down to normal and I felt fine, within seconds. Can anyone explain what had happened?