As I was working on the first exercise, the bench press, about two thirds way through the second set, I made an error on my form, and brought the bar down too low on my body (the bar is supposed to come down on the nipple line). The next push up, and my right shoulder started calling for a veto. I finished the set, and felt out my shoulder. We dropped the weight, and tried again, and it was still there. So we aborted that set, dropped the all the weight, to just an empty bar, and did another set. This time it didn't hurt, but I could still feel it in my shoulder.
So we aborted chest entirely, and did just biceps (barbell curls and preacher curls) and then finished the time on the calves machines.
I didn't feel anything go "sproing", and it doesn't hurt when it's not under weight, so I really hope it's nothing really serious, and that it heals up by the time it's time to concentrate on shoulders.