When I was about 18 I was horsing around with dh, then my bf and I punched his back. I felt something tingle in my hand and then pain. It went away for a little while and then as we were leaving our friend's house I realized that every time that I held something in that hand I dropped whatever it was. I waited until later that night and then went to the ER, it was aching in general and I had shooting pain when I moved it . They xrayed and told me that it was sprained and I should go home and wash dishes to help exercise it in the warm water. The hospital called me back the next day and had me come in, even though it wasn't painful anymore, just a bit 'off'. The radiologist had checked the films and it was a fracture, they referred me to an orthopedic doctor. I went to the appointment and was shown into the exam room, the assistant who looked at my xray set out the materials for a cast and I joked with my dh that it looked like she was going to be making a mistake ...... the Dr put the cast on about 5 minutes later.
I have had a few more broken bones since, though none of them have required casts, I don't know about the location of your injury necessitating a cast, though when my dh was climbing a play area slide in a discovery zone when we were first married and he shattered his big toe the ortho (same one, he is used to us!) gave him the option of casting because it involved his big toe and was affecting his balance so much.
I am sorry that this happened and I hope that you wake up with no more pain!
laura, dh Brian, ds Rory 14, dd Ellie 13, ds Caelan 11, ds Seamus 9, ds Finn 7 and Penelope 2 !!!!