My strained muscle?

I neglected to mention my ailment.  Sometime last week, I began to develop a pain in my right upper arm.  It was somewhat slow in developing but reached a painful level on Friday.  I had trouble sleeping that night because I like to sleep alternating side to side due to a bursa in each hip.  My arm inhibited my turning over.  It got worse on Saturday.  I could not raise my arm in a pretend flapping motion.  It was very painful to raise it above my shoulder or reaching above my head.  I had to twist my body to make my right arm do everything.  I could not even use my left arm to turn the steering wheel and had to slide my right hand up the wheel to make the turn.  This continued while Tom, Stacy, and Olivia visited and hurt more Sunday evening as well.  When they left Monday, things began to slowly improve.  By Tuesday morning I was back to about 50% efficiency and was at 90% during exercise class.  I did have some slight pain but stopped doing anything that gave me even slight pain for fear of reinjuring myself.  The mystery is what caused it.  I think I injured the arm during an exercise at Silver Sneakers a week ago.  I just hope it healed on its own and stays healed.