Ever wondered why you feel tired after a flight? When you're flying at 35,000 ft (10,670 meters), the cabin will be pressurized to about the equivalent of 8,000 feet (2440 Meters). Flying at those altitudes, the air gets thinner, and you easily get out of breath. There is less oxygen in each breath you take because of the lower air pressure, and that lower oxygen level tends to make your brain fuzzy.