Almost 2 weeks ago in my kickboxing class we did a bunch of relay-type things, including some where we all stood in a circle and TOSSED a 60-pound punching bag to each other. I had a great deal of trouble catching the canvas bag and didn't realize it until the next day, but I seriously hurt my shoulder by doing that.
I suffered over the weekend until I could get to an already-scheduled chiropractor appointment on Monday afternoon. He diagnosed that I popped a rib head and that's what was causing the incredible, searing pain in my shoulder. It took a week of seeing him every day to get back to feeling normal again.
I asked him if I could try kickboxing this week and he told me yes, but to be careful. Yesterday was my first day back (the instructor felt SO BAD about me getting hurt!). I quickly discovered my shoulder was not up to punching, so I just worked my right side. It was good to get back to sweating, though, I really missed it!