When I got my first monitor, I was shocked to learn how much CO2 was building up in rooms at home, even with just one person. I started opening windows and watching the numbers go down.
Last night we turned on the AC and closed all the windows, and I woke up at 4am feeling off. The thought that popped into my head was, "the air is bad," and then I thought, "I can't possibly know that," but I got up and checked the monitor: CO2 was way too high. Opened the windows, went back to sleep.
Since we've begun using the Aranets to keep the CO2 low, I definitely notice a difference in concentration and energy.
This has morphed into feeling a real craving to go for walks and get fresh air. I'm now basically one of those cheerful 19th century mothers who respond to everything with, "Did you open a window about it?"
Or, "Have you taken a walk about it?"