[pdc56]

I've found this too, but assumed it was placebo.

I lived at 6500' for a while - that was too high.

The sweet spot for me is a particular mountain I go to which starts at 1200m and goes to 2000 (although I don't spend time at the peak - it's a ski field).

Thanks for your anecdote, now I feel I can take my observations more seriously

[eastbound]

It could also be the sheer concentration of CO2. I work in a forest: 400ppm in the office every morning. Back at home, in the city, 5km away: 580ppm minimum all day long. Maybe cities make people stupid :D

[sideshowb]

Probably not in my case, haven't measured co2 but I am lucky to live in a small village.

[thehappypm]

Mount Washington?