I'm not dead only because I have a carbon monoxide detector in my house.
Last night the auto-fill on my boiler failed. The boiler cooked itself dry, continued to fire, and cracked. This allowed combustion products to enter the steam pipes (I have a steam heating systems), and then to vent into the house via the radiator vents. Just as I was planning to crash this morning the carbon monoxide detector went off.
So now I don't have heat, and I need a new boiler - on the upside, I'm not dead.
It also explains the headache I developed just before the alarm. The alarm went off when levels reached 15ppm, and it was climbing until I killed the boiler and vented the house.