This seems like a very odd topic to bring up. However, my wife after returning from a business trip from FL on Friday has had a bad sinus condition(infection?) and insists that this happens to her every time that she flies. 

While I think that there would be some factors in the flying that contributed(changes in atmospheric conditions for instance)  I am thinking that additional stress and getting no sleep the night before her big presentation probably ran her body down...........and made it more susceptible to getting sick. 

I just randomly picked a link that discusses air travel and sinus's below and had to laugh at one of their suggestions:

Some experienced flyers suggest drinking between five and eight glasses of water before flying.  Continuing to drink water while on the plane can also help.

That's ridiculous advice. Who could drink that much water and not have a serious problem needing to pee numerous times. . On the drive, at the airport and in the airplane who wants to have a bladder about to explode or need to poddy numerous times because they drank 8 glasses of water?

https://www.careworkshealth.com/blog/how-to-deal-with-sinus-problems-following-air-travel/

So, a follow up question might be. How much urine can a healthy bladder hold comfortably?

https://www.livescience.com/32330-how-much-urine-can-a-healthy-bladder-hold.html

A healthy adult bladder can hold up to 16 ounces (2 cups) of urine comfortably, according to the National Institutes of Health

So by taking their advice to drink 8 glasses of water(we will assume 8 oz./each) this would mean you would need at least 4 bathroom trips................1 for every 2 glasses of water.