I've often complained that flying is the most exhausting thing you can do that involves not doing anything at all. Long meetings are number two on the list...
That's from hypoxia. Being in an airliner is equal to being at about 5,000'. The reduced air density means less oxygen and you get fatigued (also reduces cognition, coordination, vigilance and night vision).
Closer to 8000' in commercial airliners. While it's technically hypoxia, insofar as it's less oxygen than at sea level, I don't know if 8000' is enough to cause the effects you're describing. Anecdotally, I'm a fat smoker, and I don't seem to notice any of those negative effects at 8000', but I certainly notice them at around 12000' or so.
I didn't realize it was that high. I guess I was remembering from the Cessna 421 I flew, but we were cruising at more like FL250. Looks like the 787 brings it down to like 6k though.
Getting exhausted from flying is not due to CO2, because a plane has more ventilation (measured in air changes per hour) than the majority of buildings.
I thought it was also due to micro movements of your body trying to remain stable. Kind of like driving a truck on a rocky road but at a much smaller scale for much longer.
I've not seen that claim before but it certainly seems plausible. It does seem less tiring if you're sitting next to an empty seat rather than a person.
The abstract says nothing about exhaustion. Does the full study?