At first I though it was just part of the marathon evil cold I'm now recovering from, to do with the pressure in my sinuses etc. That seems to have gone now and I've still got a headache 
Paracetamol or ibroprofen dull it slightly or if I'm very lucky shift it for an hour or two, but I've not taken any today. Getting rather worried about taking it for so long TBH.
I'm now really worrying and can't get in can't get in touch with my OOH doctor for a couple of hours (no NHS direct here).