[paulcole]

I wondered this too. Like yeah you’re going to be cognitively drained after being in a crowded closed meeting room for a long time. Is it because you were talking and working or because of the CO2.

[dredmorbius]

If the sense lifts immediately (within seconds to a minute or so) after opening a door or window, I'd tend to suspect the atmosphere.

[paulcole]

Good old placebo seems just as likely.