system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5 why flying takes so much out of you physically and mentally when you haven't done anything but sit there?
gpt
A few reasons. First, airplanes are pressurized to an altitude above sea level; usually between 6,000-8,000 feet. This means there's not as much oxygen as at sea level. While it's not enough of a decrease for you to be aware of, it does tax your body a bit more, especially on longer flights. If you've ever done any hiking or mountain climbing at high altitudes, you'll recognize that you get fatigued much more quickly than at sea level. Second, airplane is is very dry. This tends to make people dehydrated. Third, travel is just plain stressful. You're packed into a small area with a bunch of other people (and their germs) for hours on end subject to engine noise, various cabin noises, people bumping into you...etc.