I have not noticed the farting. I will take note.

I believe I fart more at sea level. The rich, moist air comforts me and the relaxed feeling is felt by my butt, as I release my sweet air upon my surrounding world. Aah, sweet ass air.

In addition to the air being thinner (with pressurization sometimes closer to 10,000 feet rather than a thick 8,000), there is an addition reason for feeling tired after flying: dehydration.

The combination of near-0% humidity caused by pressurization and the reduced pressure means that you are certain to lose a significant amount of water even just sitting in your seat without exercise.

Pressurizing air for the cabin causes the air to heat which must in turn be air conditioned back to normal temperatures. As a result of the process of cooling, the pressurized air is dehumidified down to nearly 0% relative humidity.

The reduced pressure increases the rate of vaporization of water from the lungs and nose with each breath.

It's this dehydration that was the original reason for serving the complementary non-alcoholic drinks on flight. That's pretty much stopped due to economics but the dehydration effects of any flight never ceased.

Then how come I feel so energetic in Breckenridge? With a 9,000 ft. base and 13,000 ft. peaks, wouldn't that be more exhausting than a plane ride? When I'm there, I just want to snowboard all day, then explore that wonderful town. I think planes are tiring, because we are crammed in there like cattle. It's very stressful.