I have this sinus problem too and I believe it has something to do with the weather or consistency of temperature. This sinus thing will "attack" me whenever there is a change in temperature, for example suddenly walk into a cold aircond room from outside hot environment and vice versa.

Also, morning time when wake up, it happens as well, I have to assume night time while sleeping, weather/temperature is low and when wake up time weather/temperature no longer the same. Weather here is not consistent, between day and night temperature is different. Been to Taiwan last year during their cold season, whole day morning till night also same cold temperature and surprisingly enough I never had this sinus problem during my 2 weeks stay there. Got to love the cold weather there!!!

I have tried quite a number of medication before in the past, including those spray and drop one, unfortunately those only could provide temporary relieve, not a long term one. I think this kind of thing no medication can fully cure one. When it gets worse until cannot tahan, I use "illadin" drop, then at least night time can sleep peacefully!

Yes, aircond can cause it, but only at certain temperature, I mean for my case. Anything 20c and below, nose can easily get irritated (meaning it's a sign the sinus problem is coming). My method to overcome this is, before sleep, on aircond first, set 20c, after 10-15 minutes only I enter the bedroom, and immediately tune up the aircond temperature to 26c, with the most minimum fan speed, then i can sleep until morning peacefully, next morning wake up won't have any sinus problem. In office also I set aircond temperature to 25c, ngam ngam, nose won't get irritated. Maybe for other people can be different, so kena slowly fine tune i guess