One...and it was successful. Carbon Monoxide.
I achieved clinical death, but was revived via CPR (ironically, by the abusive parent who's last words to me were, "All of us would be better off if you never existed"). Ended up in the ICU for three days before I regained consciousness. There's no way of knowing how long my brain was without oxygen, but I definitely ended up with brain damage and memory issues.
This was back in 1989 (I was 16), and it wasn't something I had planned out. I was in the grips of (what I now know is) severe Autistic meltdown, and I was pushed over the edge by a particularly harrowing day of targeted abuse and bullying. In retrospect, all I had to do was run a hose from the exhaust to the inside of the car and I would have been spared this ongoing hellscape. Back then, there was no way of researching these things. It was just dumb luck that my parents happened to have an old 1978 vehicle that produced a LOT of fumes.
Despite what I've read on the internet, my experience with Carbon Monoxide was fairly peaceful. In fact, I got a little bored in the car and went back inside the house for my walkman. It smelled a bit, but I just sort of fell asleep.
Family was out celebrating the 'golden child' of the family, and she opted to not have ice cream afterwards. If she did, I wouldn't be here.
Flash forward to today, and she's in the middle of a 5 week 'Sabbatical' in Europe (even though she hasn't worked in 10 years). I, on the other hand, am writing this while watching youtube videos on how to disable the CO sensor on my generator. Some things never change.
However, I'm going to get it right this time.
It's been 34 years of desperately trying to fight this. I think that's long enough.