I've had severe sinus pain only once, when I lived in Johannesburg (alt 5,500 ft). I was descending into Cape Town on a commercial flight from Jo-burg as pax. I had no other symptoms of cold, and put it down to my sinuses being 'used' to the high altitude and getting a bit of a surprise by the Sea Level pressure. Don't know how medically correct this conclusion is.
Bing: Unpressurised aircraft can be worse that pressurised aircraft. Although pressurised cabins climb to an equivalent altitude of around the 8,000ft mark, the rate of change is normally limited to a low value (I think it's around 500ft per min). In unpressurised aircraft the rate of change of cabin pressure is often two, three, or even four times this: it obviously directly depends on the aircraft's rate of climb.
Dave Incognito: Although you won't be interested in this being from Oz, UK-based people may want to know that you can buy Beconase sprays over the counter here.
[This message has been edited by foghorn (edited 15 January 2001).]