So SO sorry for your problem GJm. I don't actually HAVE that problem BUT once that DID happen to me.

I got a massage and the massuese Streched my hands sideways, both of them. I TOLD him that hurt but he said it was good to stretch all the tendons and ligaments in your hands so I allowed him to continue, STUPIDLY!! The next morning BOTH my hands were all swollen JUST like yours and I couldn't even move my fingers. it took a few days for the swelling to go down and I was totally useless in the meantime. I did soak them in cool water frequently because Obviously he did some minute damage in there and they HURT. SO if someone tells you HURTING you is good for you, tell them to STOP!!!! and get away from them. I should have sued him but he was a student and the massage was free and there was no lasting damage.