It could be food poisoning from the flight. But it could also be food poisoning caused by something you both ate before the flight. It can take up to 48 hours or more for some forms of food poisoning to begin to affect you, and stomach flu is another thing altogether.

http://www.vdacs.virginia.gov/foodsa...oisoning.shtml

You should reflect on all the food you ate in the 24 hours prior to the flight and whether you both ate/drank the same thing.

By all means, email the airline with your flight date and number. If they get other complaints, they will know something is wrong.