Consider using a decongestant nasal spray like Afrin if you still feel congested the day of the flight it may work better than Sudafed. I concur with the recommendation for Entex LA (now it's Entex PSE) from your doctor. It has a long-acting sudafed and a medicine to thin out your mucous. Tylenol Severe Congestion over the counter is similar, but not long-acting. The biggest risk with the sinus infection is that it will plug your Eustachian tube which connects the ears to the nose. You could easily rupture an ear drum. I have never heard of anyone rupturing a sinus flying, but some of the sinuses have pretty thin walls, just hope they rupture out and not in towards your brain