Girls, such a question, I don't understand what's happening with the c…

Girls, such a question, I don't understand what's happening with the child. The situation is this: when he gets upset, either I don't allow him to do something dangerous, or I do something that isn't according to his – he starts thrashing, arches his back and throws his head back. It was like before, if something didn't please him – he hit his head on the floor, then it passed. Our pediatrician says that the child is protesting in this way. I want to hear your opinion about this ??