I find that really interesting from 1k change.
We are going to Cooper over Christmas, base 9,700.
I went there a few years ago when I was turning 40 and worked out like a madman (for me) out of fear of altitude sickness.
I was ok except huffing on some hike to at 12.200 feet(?) but did wake up a bunch at night.
My understanding is all this is caused by less oxygen by volume in the air, causing increased respiration, causing mor exhilarating, causing more dehydration, causing headaches and eventually altitude sickness if you don’t hydrate.