My baby keeps bumping his head whenever his crying or angry.

My lo is 19months old. Its was started when he was 1year old. He keeps on bumping his head on the floor or on the wall accidentally that is why we comfort him. Hug him. He feel safe whenever it happened. And now when he doesnt get what he wants or does bad thing like hurt his sister and we get mad at him something like that. He cry and hurt his head bump it on the floor or wall. So i cant stop myself from comforting him so he will stop doing it. What will i do? Im really worried. Thank you so much.