I have, for over 2 years, had a spot on my scalp (well, sort of under the scalp) that feels like someone smacked me in the head while I slept.
It's only sometimes, and things that seem to aggrevate it (meaning make it hurt more, as opposed to make it hurt) when it's going on is anything with pressure, from touching, brushing, etc, right up to even bending over (increasing pressure to the top of the head).
I have NO clue what it is, but I'd love to know too.