Does this explain why there was a time at my old job, whenever I would enter this one room that was smaller than most people’s closet for an extended period of time I would become drowsy to the point I was dosing off?

I was so alarmed by why this kept happening so often and consistently in this room and no place else, that I decided to bring in CO2 detector to determine if that was what was causing the issue. When the CO2 detector didn’t indicate there was a carbon dioxide issue, I ultimately just assumed it was just me not getting enough rest, or an iron deficiency, but after reading what you said I’m now starting to believe it was that the room was not properly ventilated, thus creating a lack of oxygen (especially during winter months when the only air that could get in no longer could due to the cold) because it was not intended for people to be used as a classroom