It's possible to OD on meth - just not as likely to die the way a Heroin OD would do it, because meth does not cause CNS depression.
Your heart and lungs won't slow down too much, the way an H overdose happens. But you could have a heart attack, collapse a lung, have an aneurysm, a stroke, or many other gnarly outcomes.
I used to slam H and Meth together, very recklessly, and on numerous occasions I would slam the shot and immediately pass out, hit my head on things, wake up confused, forget I just did a shot and do another and pass out again. I had to be physically prevented from
doing another shot by a friend who was watching me do this stupid shit in a motel room. Dizziness, fever-like feeling, heart racing, even start nodding out but in a totally different way than Heroin - like an uncontrollable urge to sleeeeep.
The way I would describe the sleepy feeling was feeling like you're going to straight up FAINT from
being severely overwhelmed very suddenly. Fainting. Not a cool feeling.
Where I'm from, we call that "over-amping". I used to see it happen often, actually - most often to strictly meth users.
The ones like me who mixed H into their shots always had that edge taken off it by the H.
When you do a lot of shit at once, IV, it travels via your veins to your heart and immediately to your lungs, where normally carbon dioxide is traded out for oxygen. In the case of a big meth shot, it's like carbon dioxide AND meth is somehow exchanged - as if the CO2 somehow conjugates the meth molecules in your blood and is able to turn them to vapor and push them out along with the CO2, resulting in that feeling you're talking about.
We call that "the cough" because it feels like your lungs suddenly fill up with a kind of icy vapor like you
just inhaled some dense fumes, and you need to cough it out. It's usually interpreted as a sign that you did enough lol but doing that much usually means you're going to have some effects that are unheard of in small shots or any smoked amounts. Head swimming, almost like an MDMA rolling feeling where you're sluggish and sensitive and liquidy.. IMO the cough means you did too much. Don't do that again.
I would highly suggest you never do that again. Ever. I've had seemingly healthy friends have brain issues, heart issues,
one guy's fucking right lung collapsed after a major shot right in front of me, he starts fishing out kind of, and gasping for air - ugly sight.
He survived but barely. Very very bad stuff, man. STop it if you can.
If you want to read a pretty crazy trip report of what happened to me when I overamped after slamming H and meth all day after having been awake for 2 days, check this insane shit out. Perhaps living vicariously and NOT doing any more meth might entertain your mind a bit?
http://bluelight.org/vb/threads/804752-(Crystal-Meth-0-5g)-(BTHeroin-0-2g)-IV-Very-Experienced-3-Choices?highlight=experienced+choices
If you are interested in getting sober or at least attempting to repair yourself,
check out the thread I just started a couple days ago, where I'm creating a guide
based on my experience so far in trying to repair from years of IV drug use
http://bluelight.org/vb/threads/817897-How-To-Repair-Your-Body-Mind-Soul-A-Guide
Good luck man. Please be careful.