From this thread it sounds like the best way to off yourself is with IV heroin. Not exactly the best thing to learn on an HR forum :/
I OD'd on ketamine before. My friend was converting 2g ketamine to 100mg/mL solution but didn't label his vials. I ended up drawing from the wrong vial, doing an IM injection that was basically 1.5g of ketamine instead of 50mg. My friend said he had to lay me on my back and tilt my head backward because I wasn't breathing properly. My experience was everything started to turn white and I knew immediately that I took too much. The last thing I said was, "Oh fuck I'm gonna K hole" and then everything went white. I didn't even have an out of body experience, I just remember being gone and then suddenly coming back. When I came back, it was like being a robot and having the switch flipped back on.
MDMA is another I've done too much of. Passed out right in the middle of a rave and I had to be dragged to the medics. My heart rate was incredibly high and I was overheating. They had to give me an IV and heavy sedation to calm my body down. It was really disorienting... because on the one hand I was rolling so hard that it was kind of blissy, but underneath the bliss there was something terribly wrong and my anxiety was high. The two feelings mixed together were so fucked up.
Although it's not really possible to OD on acid in the true sense, I accidentally did 1mg of LSD one time thanks to a dilution problem with liquid LSD. It was the worst experience of my life and I was psychologically fucked up for 6 months. While tripping I couldn't move, couldn't talk, couldn't make sense of anything. Remember that classic commercial "this is your brain on drugs"? Yup, it was kind of like that. I would look at my limbs and they would be dissolving into the floor around me. Nothing made sense and there were no boundaries. My brain was putty. It was also incredibly exhausting. All I wanted to do was close my eyes and sleep but it was impossible. Eyes open or eyes closed the visuals were so bombarding.
I had alcohol poisoning as a teenager... drank two whole bottles of Canadian whiskey on a dare. Dumbest thing ever. Had to get my stomach pumped and stay in the hospital for a day. All I really remember was being paralyzed and too weak to even roll over when I puked, so I kept puking all over my face and neck, and choking. My friends (who were 14) at least had the sense to tilt my head to the side, but they NEVER went and got help because they were afraid of getting in trouble. So I laid there paralyzed, puking and pissing myself all night. My father walked into my room in the morning and smelled the wall of puke and booze and was like WTF!!! Hours had passed but I still got rushed to the hospital where they did the nasty coal tar stomach pumping thing. I wasn't able to touch a drop of alcohol without getting nauseous until I was like, 26 years old.
Now that I'm writing these experiences out, I'm wondering how the fuck I've survived to this day? Drugs are intense!!