According to Richard J Kinch :
Greg O writes:

So in other words, a few years ago when I was working on a car, in a
closed shop, exhaust hose attached, but unaware of a hole in the
exhaust, I should have known sooner I was poisoning myself?? I
realized that I was feeling faint and headed out the door. I don't
remembering even getting outside, don't remember opening the heavy
shop door. All I remember is a buddy that happened to stop by, finding
me sitting, passed out in a snow bank along side the shop. If I had
not caught myself feeling faint, or the shop door was farther away, I
would not be here today. I noticed nothing untill I felt dizzy.

Who knows, but sounds consistent with slow CO2 anoxia,

No shortness of breath. Not slow CO2 anoxia.

CO poisoning.

Much more consistent with CO.
--
Chris Lewis, Una confibula non set est
It's not just anyone who gets a Starship Cruiser class named after them.