I have no idea how I sprained my hand. It's a minor sprain, but it is still damn inconvenient to do any little task. My middle finger started to ache around the knuckle yesterday while I was at work. I thought it was odd, but it didn't seem to be serious. By the time I left for the day I couldn't use my hand much at all. There didn't seem to be any swelling, but I could no longer close my hand nor open it completely flat (so much for yoga this week).
Now it's swollen around the knuckle and I have limited movement. For example, typing is a little challenging as I can only use my index finger and thumb on my right hand.
The good news is I don't see this keeping me from running so I'll be heading out for a run today after work.