I read an article that showed that 100% of people that failed a suicide attempt with carbon monoxide described it as being worse than being slowly killed, it also says that the majority of people say it feels similar to being tortured to death. I would personally not choose this method. Ive also read reports of people waking up 5 or 6 hours after trying to kill themselves with charcoal with raging headaches, nausea, throbbing throats ect. I think there are better ways to go.
This is a quote of somebody's post from here:
Until recently, I had no doubts that CO poisoning if done correctly is a peaceful, painless method with high chance of success, however I found some resources, which make me question it. In particular this website seems to provide information on that issue:
https://web.archive.org/web/20090212121445/http://www.geocities.com/monoxidemachine/
To quote
Further more
I'm very aware, that this is just some random blog from 2009 mirrored on the Internet Archive, quoting some nameless, supposed specialist, but since I want to be really sure, I want to know if the experiences of the people here, who survived CO poisoning were anything like this.
Other resources like the PPH by Nietschke (who the above article is a critique of) say it's peaceful.
The ASH Wiki is rather nuanced (which I don't know if it's a good or bad thing) and claim it's neither peaceful nor absolute agony and states the potential discomfort, one might experience.
Link:
https://web.archive.org/web/2014061...w_does_carbon_monoxide_work_as_a_lethal_agent