Yep, me too.  I get it often.

The only sense I could make of suffering the same/similar thing was that it
could be something to do with the rising/changing humidity as the day warms
up. (ok, spose ur going to tell me it's icy winter where you are living :)).

I frequently have problems with humidity change affecting my sinuses....to
the point of real spin-outs.  I get problems when going near the
refrigerated section of some supermarkets....much of my beliefs are based on
un-scientific evidence.  I'd had various tests done to try find what was
causing the spin outs....epilepsy & anxiety......but I believe in hindsight
that it's all due to my sinuses.

To me, the changing weather patterns of your particular locality should be
checked out.  Here in Queensland, Australia there can be pollen-laden dryer
breezes off the local hills, northerlies blowing dust & pollens from the
desert, sea breezes & southerlies blowing up some pollution from the city,
or just plain old clean sea breezes.

I also used to live in South Australia where there was not much humidity,
but there'd be frequent changing wind conditions.  I had more sinus probs in
SA which is the worst place for asthma sufferers, apparently.  A few people
there told me that the dust often blown around was pretty bad because of the
soil type.

I still get probs from refrigerated air-conditioned rooms & the supermarket
fridge sections, & so just avoid being "trapped" where possible.
I also had heard of  "damaged sinus / airconditioner-sensitivity" many years
ago even before I realised I had such problems.

Hope this is of some help to you.

cheers,
Rob