[RKDinOKC]

Flying thing is complete and total BS.

First, why would thay pressurize the cabin any more than normal!
When they call it a pressurized cabin it means the pressure is higher in the cabin than outside the cabin.
Not that the pressure is higher than it was when they closed the door to take off, ie normal.
So no, it does not compress your body.
Might as well say going over 100mph compresses your body against the seatback.

Yes they let air in the cabin because it has more oxygen than the stale air inside the cabin.
No they do not take the air from the engine exhaust, that is typically behind the plane.
And it is just Air, it is not processed to add nitrogen. Why would they, it is not a space ship or a diving bell (they use helium).
Air is already 79% nitrogen you are breathing right now!!! Ahhhhh.
You should be more concerned that they actually do open the fresh air vents!
If they do not the oxygen level drops enough to make everyone sleepy. Zzzzzzzz
Sleepy is about it though.