You could of brusied something, or might have a slight concusion.
Assuming equal velocity, I'd say the coconut.
Hitting it with a hammer
Your head hurts is a declarative sentence.
No
Cancer
did you hit your head? ....
Either face of the head is the hitting surface.
Falling and hitting your head can cause a fracture of the skull, bruising of the brain, unconsciousness, disorientation, delirium, and possibly death. Alternately, a concussion, which shakes the brain inside the skull, can cause short term confusion. Both require medical examination.
There are infinite potential sentences that can be created with the word head. Here is a short example. Person one: "My head hurts." Person two: "My head hurts too." Person three: "My head hurts more." Person four: "She said her head hurt, yours hurts too, and his hurts more." Each person can just add a word, or change a word to any current sentence and that will create a new sentence.
If it hurts
Take an aspirin