I would like a medical expert to explain how this works.
I had some serious surgery a while ago, and I was on home oxygen for a while. As I recovered, I needed less and less to function. After a while, I was only using it at night, only 2 liters a minute. I absolutely needed it, though. I tried going without it, and when I did, I would wake up at night in a panic, take my pulse oxygen reading, and find it in the low to mid 80s.
As I approached a planned month-long trip while still using 2L per night, I expressed my reservations to my doctor. He explained that those nissing 2L of O2 per night would be compensated for by the fact that I was going from my normal mile-high elevation to sea level. Sure enough. the night before I left was done without that oxygen, and it was brutal for me. The first night at sea level was just fine.