?The pressure, temperature and oxygen levels in the cabin fluctuate, and the humidity level is lower than it is at sea level,? says family medicine physician Matthew Goldman, MD. All of those things can mess with some of your body's normal functions.

The "weird" feeling you experience on a plane is primarily caused by barometric pressure changes and vestibular discord. As the aircraft ascends and the cabin is pressurized to roughly 6,000–8,000 feet, the air in your middle ear and sinuses expands, leading to that "clogged" or popping sensation. Simultaneously, the lower humidity (often under 10%) can cause rapid dehydration, leading to fatigue, dry eyes, and a "foggy" brain. Furthermore, there is a conflict between your eyes, which see a stationary cabin, and your inner ear, which senses the subtle vibrations and tilts of the plane; this is a form of mild motion sickness that can make you feel nauseous or dizzy. In 2026, many modern jets like the Boeing 787 Dreamliner and Airbus A350 mitigate this by maintaining a lower "effective" cabin altitude and higher humidity levels. However, the psychological stress of being in a confined space and the disruption of your circadian rhythm (jet lag) also contribute to that general sense of "unwellness" or "plane brain" that many travelers experience during and after a long-haul flight.