Depending on your symtoms, and other basic health, physically. Perhaps a sudafed 20 minutes before you take-off and then every now and then depending on the directions on the box. There are various types, some dry you up, some make sinus's drain, some are for high blood pressure, see what works for you. There are also other brands and products that do the same thing.

If you were not having any sinus issues before you boarded the plane; ignore the above. Much too complex to diagnose with what you have written.