Anacrusis, You were lucky you didn't stop breathing. For people who get such severe symptoms while flying, it's recommended that you have oxygen while on a plane!
I researched this quite awhile ago because I knew I was having trouble while in an airplane. There's also a vignette in my book about it.
It doesn't matter if you felt better after resting awhile or after taking Mestinon. You need to find a pulmonologist and get checked out. There are cardiac conditions that can cause hypoxia or hypoxemia too. There are some people who have pulmonary hypertension and don't even know it. In order to determine if someone has it, a cardiologist will order an echocardiogram.
I have taken an oximeter on airplanes to see for myself what is happening. If I sit in my seat, I'm relatively okay. My O2 hovers around 88%. It can go lower. And my pulse increases, which is the heart trying to get me more oxygen.
When I get up to go to the bathroom on a plane, my O2 goes into the 70's. On one trip, I got a "little" chest pain and was dizzy. I even took photos of the "events" to show my pulmonologist.
The severity has to do with air speed, altitude and pressure. They save money on fuel by manipulating those things. And do you really think they want you to stay hydrated because the cabin air is so dry? Nope, they want you as hydrated as possible so that your veins and arteries will be as dilated as possible so you won't have a heart attack or stroke and screw up their schedule. Or sue them!
Good instincts, wild_cat.
Heat Intolerant, Have you ever had an echocardiogram? You need to figure out why this is happening!
Your brain scan while sitting still on the ground is a lot different than your brain - and other tissues - while up in the air, experiencing low O2!
Isn't it nice of them to think about the pilots?