I opened my shop in 1978, and was willing to do about anything. I was tuning up my first ex-wife's '76 VW Rabbit [she'd left me because she didn't want to suffer through the start up]. It was COLD out, late evening, I was alone, and I didn't want to open the door. My rubber exhaust hose wouldn't fit through my new aluminum exhaust port in the door, so I stuck a piece of steel exhaust pipe in the end of the rubber hose [as a reducer], and put the steel pipe through aluminum ring in the door. This was a carbureted Rabbit, and it had been fouling plugs. I had it running pretty well, and thought I'd give it a few more minutes run time so I could watch the choke open and set the idle. The next thing I new, I just decided to sit down at my desk and take a nap. It seemed like a great idea. I sat down and put my head down to sleep, just like that. For some reason I woke up and thought , "This is weird, you've never done this". I got up and the shop was full of exhaust. The metal pipe had slipped out of the door. I opened the doors and was OK later that evening, but I'd just about bought it because I was in a hurry and not paying attention. Carbon monoxide is insidious, it's like a drug or a tranquilizer. Watch out - it loves stupid.