h2g2 The Hitchhiker's Guide to the Galaxy: Earth Edition

Apart from the health impacts from jet lag, which has its own h2g2 article, there is another way you can get sick on a plane, and you are exposed to this danger regardless of where you are. The food is your enemy. Hot meals that are served on an airplane must be cooked on the ground, then loaded into the plane while being kept in warmers, and served up to a couple of hours later. The foods are not maintained at a temperature which could arrest the development of bacteria, and thus poses a risk of food poisoning to the passengers. I myself suffered this on an international flight... however, I contracted it on the Los Angeles - Chicago leg. If you want to be absolutely safe, eat only things that have their own plastic wrapper, or are not heated. Eat before you leave, after you arrive, and if it's a particularly long voyage with stops in between, at the airport concession areas.