Masks don't cause CO2 poisoning. They do decrease the partial pressure of O2 during inhalation, and the partial pressure of CO2 during exhalation, but sitting in a room with the window closed would have a bigger influence on your CO2 levels.
As far as I know, cloth masks don't affect oxygen intake or re-circulation much, but the N95 can definitely have an impact (20% less oxygen, if I remember correctly, not sure about CO2).
There was a single instance where I was with someone who insisted that I wear an 95 AND a cloth mask on top of that. It was only for a few hours, but when I got back, I was pretty lightheaded and I had definitely been breathing a decent amount of recirculated air. When taking just the second layer off, I could feel the outtake through the filter, but when I put the second layer on, everything had to come out the sides (there are normally no gaps, but I guess the extra obstruction made it easier to push the mask outwards rather than just go out the filter), so I suspect that not a lot was getting in either. Their idea was definitely stupid, and I am definitely never doing that again (I don't have much experience wearing a single N95 so I can't comment on how much worse the combination made it).
Masks don't cause CO2 poisoning. They do decrease the partial pressure of O2 during inhalation, and the partial pressure of CO2 during exhalation, but sitting in a room with the window closed would have a bigger influence on your CO2 levels.
As far as I know, cloth masks don't affect oxygen intake or re-circulation much, but the N95 can definitely have an impact (20% less oxygen, if I remember correctly, not sure about CO2).
There was a single instance where I was with someone who insisted that I wear an 95 AND a cloth mask on top of that. It was only for a few hours, but when I got back, I was pretty lightheaded and I had definitely been breathing a decent amount of recirculated air. When taking just the second layer off, I could feel the outtake through the filter, but when I put the second layer on, everything had to come out the sides (there are normally no gaps, but I guess the extra obstruction made it easier to push the mask outwards rather than just go out the filter), so I suspect that not a lot was getting in either. Their idea was definitely stupid, and I am definitely never doing that again (I don't have much experience wearing a single N95 so I can't comment on how much worse the combination made it).
It's like living at higher altitude. Your body adapts to the lower partial pressure of O2.