It's a real stinker.
Not sure what kind of headache it is, it hasn't presented like one of my thankfully rare migraines - no visual weirdness, only a little nausea.
Just like a band of pressure around my head, like a hat of pain, especially across my (watery) eyes and temples and the back, at the base of my skull. Tension headache probably, although I'm not sure why that would wake me up and I don't feel more stressed than usual.
Mostly just the ghost of it now, though, so hopefully that's the end of it.