When you fly the gasses in your body start to expand. The cabin of most commercial airplanes have a pressure of around 10,000 feet. That allows the lighter gas in your body to expand. Causing pressure in your body and needing some way to escape. Only 2 ways out.
Have you noticed you tend to want to fart on a plane. Some times quite often. You see i am a flight attendant for an airline and i tend to get jet belly a lot. its not my fault i need to fart when i am handing you a coke and a bag of nuts. Enjoy the extra gas in your club soda next time you ask for a drink.