Blame it on the air pressure. At cruising altitude, our blood absorbs less oxygen, which can make us sleepy, dizzy, and mentally fuzzy. So, get up every hour and do a couple deep knee bends or lunges to boost the oxygen in your blood. And eat spinach, which has B‑vitamins that boost the supply of oxygen-rich red blood cells to your brain and muscles. And getting gassy on a plane is also due to reduced air pressure. It causes gas to expand in the body. So avoid carbonated beverages and high-fiber foods, which will increase that gas even more.