Mystery Injury

I was cleaning the apartment this morning, maybe a little more thouroughly than usually in anticipation of a visitor who will be here tomorrow, when suddenly the top joint of the middle finger on my left hand started to hurt. It puffed up and turned blue. I don't recall hitting or hurting it. It just suddenly did that on it's own, it seems. Now it's purple and still puffy. It feels like I bruised it, but I have no idea how. Maybe this means I shouldn't clean anymore.