system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: No pain during brain surgery, but why are headaches common?

ELI 5: How is it possible to have open brain surgery while fully awake (not narcose) with drilling and other rummaging in the brain goop (as apparently there are no nerves). 

But a lack of coffee or water or whatever gives me a feeling someone is hammering nails into my eyes or other parts of the head?

This question is actually my follow up (didn't want to hijack the other ELI5) to another post about headaches location. I am wondering about this for quite some time.
gpt
Because a headache isn't a "brainache" The source of the pain isn't inside your brain. While the brain itself cannot feel pain, the face, eyes, ears, sinuses, neck, scalp, skull, and jaw areas as well as the meninges (membranes that surround the brain) are full of blood vessels, muscles, and other tissues that contain nocioceptors (nerves that sense pain.)