Drink lots of water during your flight. Airplane cabins are extremely dry and dehydration makes it tougher to recover. If you're not sure you can get water on the plane, purchase some at the airport after you go through security; you can't bring liquids in large amounts through the security checkpoint, but you can purchase them afterward. Continue drinking water once you reach your destination, and stay away from alcohol or caffeine on the plane; both are diuretics, which further dry you out.
