Definitely hard to do at home, but it's not all that easy to notice in certain settings. For instance, indoor and greenhouse agriculture where pumping CO2 into

Definitely hard to do at home, but it's not all that easy to notice in certain settings. For instance, indoor and greenhouse agriculture where pumping CO2 into the room is routinely done. I'm not sure that I've experienced CO2 poisoning per se, but definitely higher-than-safe levels of it. We were installing new air quality sensors at an indoor farming facility when we (eventually) discovered the existing CO2 alarms were malfunctioning. The symptoms came on fast and immediately affected my ability to think. The first sensors we installed reported something like ~6000ppm, which we assumed to be a calibration error because no way people had been working at those levels. Didn't even occur to us it was accurate. A few minutes later I remember just staring at another sensor unable to decide which way to install the battery. We didn't even realize something was wrong until I went outside for a few minutes. EDIT: grammar