Oh My Aching Head

I don't know why I was so ungraceful yesterday, but somehow I managed to run into various things with various parts of my head, in fairly rapid succession. First, I hit the back of my head on a fire alarm. Then, while putting my sheets back on my bed, I ran into my lamp with my forehead. And later, while sitting in the back of Jess's bug, I hit the side of my head on that piece of plastic that I hit my head on every time I am in her car. So why then does my elbow hurt this morning, but not my head?