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
It's incredible how quickly CO2 can build up inside a room. I'm also in a small village, and CO2 is 420ppm-ish outside. In my home office right now with the window open but no through flow, it's 1800ppm. If I close the window, it'll head off the scale of my CO2 monitor, above 5000ppm. Now that definitely is in the realm of cognitive impairment. I need some better ventilation.
Fair. My appropriate point of comparison (if I wasn't currently nitrogen drunk) should in fact have been mountains <1000m. Which I also love, but they don't have that clear headed altitude feeling.
