Hi,
with complete combustion, a normal flame doesn't produce much Carbon monoxide, it is mostly Carbon Dioxide, which is not actually poisonous.
Yes, if there is enough in the air you can be deprived of Oxygen, and that is not good, but you will not normally have ill effect of Carbon Dioxide suffocation from a flame. If the flame has enough oxygen, so do you, (usually).
Carbon monoxide is one atom of Oxygen short of Carbon Dioxide, i.e. in a yellow burning flame without much oxygen there isn't enough to complete the combustion and the dangerous monoxide is produced.
This has such an affinity for Oxygen, it will literally rip it out of your blood stream in your lungs whe you breathe it, and in doing this it damages the haemaglobin (red cells) to the point where they are now not capable of carrying Oxygen any more.
i.e. Carbon monoxide does damage to your blood cells and isn't repairable, you are now oxygen deprived until either the red cells are replaced or you are treated in a hyperbaric pressure chamber at about 1 atmosphere positive pressure and you are given a stream of pure oxygen to breath to saturate the remaining red cells capable of carrying oxygen to the body.
It can take a long time to fully recover from the damaged red cells, they take time to reproduce, and a person can suffer further damage after they are returned to normal fresh air.
A person suffering sever Carbon Monoxide poisoning will exhibit blotchy red patches of skin where the damaged blood pools in the body on death.
Disclaimer: I'm not medically trained, this is just what I have picked up working in a medical environment as a technical officer.
cheers