What the heck?!

When Devin gets upset the way he lets us know is he bangs his head on the ground. He bangs, rubs, slides, inflicts bodily harm to himself. He had an episode on Wednesday and had a scab on his forehead. It was taking a while to heal. On Saturday he got upset again when I made him come upstairs. He came upstairs and banged his head on the ground, taking off the scab and bleeding on the carpet and had it dripping from his head. I had previously talked to our pediatrician about it. He said in the all the years he has been a doctor he has never seen a small child seriously injure themselves on purpose. There is a line of hurting oneself just enough to get attention without causing too much pain. I did wonder as I was cleaning the blood off of his forehead and out of the carpet. Should I be worried?