Accidentally hit my head 12 days after my FUE hair transplant, blood came out. Did I loose many grafts? (photos)

In my opinion I believe the injury did not disrupt the healed grafts at 14 days. It is possible but I have faith that you are fine.

If the injury was severe enough to cause normal hair loss, then it may be an issue.  Sometimes if you dislodged a graft it may bleed and that area may not grow.  There is no way to say how many grafts you lost just by a description on the Internet. 

If you have a bleeding and blood came out after you bumped up your head , probably you may
missed a couple of grafts with dislodgement of them. So I advise you to have a
visit your doctor.  

At 12 days, hitting your head with bleeding may have cause some graft loss but by that time the grafts should have been secure unless you had heavy scabbing present at that time

At 12 days post-op, you should be safe. You may have dislodged some grafts, but I would say it is unlikely. If the area was not cut enough to leave any scarring after it heals, you should not have any lasting damage. It is always best to follow up with your doctor though to have it looked and confirm.