I made one critical mistake: it hurt a lot to try to sleep so I tried to sleep on my back one night, and that cost me dearly: the active area of the lungs is not symmetrically divided between front and back, the back part has a larger active surface. Fluid then migrates from the front to the back pooling there leading to less gas exchange. I suspect that this was the lowest point and after that sleeping on my belly at least kept me safe. The really stupid thing: I knew this already (had double pneumonia when I was in my 20's).

Yeah, when I had Covid my wife was doing everything she could for me... hydrating, vitamins C and D, so on, but I think the treatment with the biggest effect was resting face-down. The fact that that is now pretty common knowledge has probably saved many thousands of lives.