How high do you fly?

[Pace]

I am no expert but know that people who live at 10 k will get used to living on less oxygen and the body compensates by increasing the red corpuscles in the blood
Surely the same would apply to smokers although they have self induced at sea level

On the question of what appears high I think it's what you are used to ? In my 150 days 2000 feet was norm the day I went to 5000 feet I felt very high
Now in a jet 10k feels very low )

Pace