My little girl is seven months but does not cry if she bumps her head ?

My daughter was with her baby sitter the other day and fell out of the car seat and hit her head on the center console ( the car seat was not buckled in the car yet but she was buckled in the car, the baby sitter was putting groceries in the trunk) but she did not cry not even a whimper! Then the other day she was playing in her bouncer she threw her head back and hit it on one of the toys and didn'ts cry but yet if she hits her arm or foot she crys should i be worried or does she just have a really really hard head! She also gets mad during tummy time and will bang her head on the floor!