Hit my head 5 days after hair transplant, have I compromised something??

If the injury was severe enough to cause normal hair loss then it may affect your transplanted hairs.  If you are concerned, it is best to contact your doctor.

if you hit your head after operation and it bleed, than it is good to see your hair surgent, you might have caused damage. But in your case, if it didn't bleed, than there shouldn't be a permanent damage. For extra precaution upload photo. 

Usually by the 8th day, the recipient grafts are secure. As you did not see bleeding, that tells you that you probably did not damage to it