I was sitting on a fence and fell down about 6 feet forehead first onto the sidewalk.

I had a ~10lb log dropped directly onto my forehead.

Needless to say, I have funny bumps on my forehead

I was concussed by a mate once. We were at a party, he went to kick a balloon and I went to header it - neither of us made it. There was a bit of blood out the back of my head but I thought nothing of it as it was only a few spots. Four hours later I'm rolling about on the street outside the restaurant and an hour after that I wake up in casualty. Yet it wasn't painful, just frightening.