Even though your brain can't feel pain, thingies in your head are installed to compensate for that.
Once I thought your head starts to hurt when your brain is tired. I can't believe this any more. Several times I happened to skip sleep completely - while intellectually working (not just watching TV or something like that). The next day I didn't go to sleep to prevent breaking the day/night biorhythm. Yet I don't remember any headaches from not sleeping enough - and working instead.
However, when I was worrying about something deeply I often got a headache to the top. Also, you get headache when you're ill. You get them after drinking too much alcohol (or getting poisoned by some other things too as I've heard).
As non-biologist I believe that pain receptors are triggered when whatever they're guarding is damaged. Also I thought that they're installed so that you can do something about the cause of the pain - that doesn't seem possible in case of headaches.
But I do hope that headache doesn't mean that my brain is sustaining damage.
So what's triggering pain sensors? Is it a chemical/hormone that is released when the organism feels endangered (by illness or something else)?