My son tends to end up in the hospital after plane rides because his allergies act up and the cabin pressure forces the infections deep into his sinuses. Tell your folks that, if they give you a hard time about taking OTC allergy meds. The Orlando hospital is a lot less fun than Disney World and even more expensive.
What he took on the way to my mother's funeral (too far to drive) was Sudafed, Benadryl, and Advil. Sudafed (pseudoephedrine) is a stimulant that also helps open nasal passages. Benadryl (diphendydramine) is a decongestant that as a side effect, can put you to sleep. Makes a good combination. Advil is advil. He got thru the flights okay.
Diphenhydramine, btw, is the "sleep" ingredient in Tylenol PM.
Benadryl (diphenhydramine) is often used on little kids to help them sleep on plane rides, as it not only helps their breathing but also can knock them out.
Good luck.