What Causes Sudden Swelling And Bruising In The Finger?

Hi Doc - Sitting still doing nothing but watching TV w/the family last night and suddenly felt a slight tenderness in my left hand ring finger, looked down and was able to watch it visibly swell and bruise before my eyes, reddish/purple from the middle of hand up to the first knuckles on my pinky and ring finger. Immediately iced it and after an hour did not disappear, but looked significantly better. Fine this am, but by the time I arrived at work - reddish/purple bruise again. Does not hurt, no apparent cuts or bites. I m 48, in moderate health. Thoughts?