Maybe he ran into a window thinking he could get outside. Dogs are dumb that way, the same way they will chase a beam of light on the wall. Keep an eye on him and if it gets worse, get to a vet
What Is The Large Bump On The Top Of My Dogs Skull?
It could be a tick, try pressing a hot piece of metal on your dogs bump. If that doesn't work, then it could be an abnormal growth. If your dog was nutured or spayed, then it's perfectly normal for that bump to be there so relax.