I bumped my head one day after my hair transplant, should I be worried about damage? (Photos)

If the injury was severe enough to cause normal hair loss then it may affect your transplanted hairs.

if you hit your head and blood came out there can be some damage. It is better for you to get in touch with your doctor and get his advice. 

If you have a bleeding and blood came out after you bumped up your head when you were in air plane or getting in a car or bus, probably you may missed a couple of grafts with dislodgement of them. So I advise you to have a visit your doctor.