I OD'd on heroin the second (and last) time I ever tried it. I got my then boyfriend to shoot me up because I felt trapped living with him (a sociopath, and a junkie to boot) and had nowhere else to go. He'd gotten some black tar on Silk Road. As soon as the shit hit my veins, my brain felt overwhelmed, like when you take a huge bong rip but x100. It felt like my brain was drowning in chemicals and I kept trying to clear my head by shaking it but it wouldn't clear.

The boyfriend invited me out on the porch with him while he had a cig. I got up and walked a few feet to the front door. It was really hard to focus on walking in the few seconds I was up and mobile since my brain was going nuts from the dope. I tried to grab at the door handle and failed a couple of times before black clouds rolled into my vision. I remember feeling intensely sleepy before I blacked out.

I woke up to paramedics bagging me and they'd cut my favorite shirt off me, then I was loaded into the ambulance where I shivered uncontrollably despite it being the middle of summer. One of the emergency folks told me I was a 3 on the 1-10 scale of being alive when they got there. So yeah, my almost-dying experience consisted of feeling really sleepy, passing out, and waking up. And having a dent in my ass because I fell on something when I went down. I think the worst part was coming to and still being in that situation with that scumbag. It made me wish a lot that I'd never come to. Thankfully I've improved my situation since, but whenever shit gets rough I still think about how awesome it would be to just feel really sleepy and just not have to dick around with this bullshit that we call life anymore. It feels comforting to know that if nothing else, at least death is a certainty.

TL;DR: almost dying consists of passing out and waking up feeling like garbage