Is injecting an air bubble into a vein to stop the heart real or a myth?
https://en.wikipedia.org/wiki/Pulmonary_embolism is very real, and can be extremely fatal if severe enough, and contrary to prior statements is not especially horrible. You will be unconscious very rapidly. Chest pains and shortness of breath are probably no different to any other heart attack. IMHO, if you live in a country with needle exchanges I could see this being a very simple method and probably a lot easier than hanging if you can't afford fancy drugs. Of course personally if I was going to stick myself with a needle I'd rather it be loaded with a massive dose of benzos and opiates, but beggars can't be choosy.
A lot of long-term heroin addicts will have some experience with minor embolisms as often their hit goes foamy when it's cooked up, and if they're hard up enough very few will toss it as a result. Some will just try to pop the biggest air bubbles with a sterilised pin. Some don't even go that far, or they try not to inject the foam, but sometimes it's all foam. Sometimes this will cause a minor embolism which is seldom fatal, and barely noticeable when you're very baked. Sometimes not so much.
I was locked in a bathroom with someone who died like this. The fact that he was smashed off his face probably helped make it peaceful but nobody even realised until someone went into the bathroom and found him cooling on the toilet. Stupid me went inside to give him CPR and got locked in with him so someone would be present to talk to the police, because everyone else was afraid of being busted for possession. They also deadlocked the front door so when it became clear he meat I was able to break the lock on the bathroom door and had to go out a window.
Incidentally, CPR is horrible. People vommit on you. At the very least they puke up foam. They've almost always voided their bowels and bladder. A cool human mouth is one of the single most disgusting things on the planet to touch. And compression, if done properly, breaks ribs, and you can hear them crunching while you do it.
Other Methods:
1. I think someone mentioned this, but which is very popular here (and nobody knows how many fatal accidents are actually suicides, some estimates range up around 30%) and that's a deliberate car accident. Not dissimilar to falling. As long as you're doing over 17 meters per second (and even crappy cars can do twice this) and you hit something solid enough to completely arrest your momentum you've got pretty damn good odds of dying. If you don't want your body mangled you can even leave your seat belt on if you're going fast enough. If the deceleration is rapid enough it will rip some of the larger internal arteries, which is a primary COD in high-speed accidents and falls where there are no head injuries. You can make it an absolute guarantee by wedging something solid between the wheel and your chest. Obviously make sure it's not too thin if you don't want to be impaled. You could easily do the same thing with a bicycle; just pedal up to high speed going down a steep hill into a wall or a parked truck. You can even take the break pads off before doing it. No fancy helmet is going to stop that killing you especially as you're almost certainly going in head-first.
2. lots of people complain about being unable to get firearms, but gas-actuated nailguns are just as deadly and widely available. You can even hire them in many places. On that note If you have access to ammunition (much cheaper and more widely available than a firearm) a zip-gun that will fire a single round through a piece of pipe (even PVC) is extremely easy to construct. You can even drill open smaller rounds and use the powder, some wadding, and a bunch of ball-bearings to make a home-made shotgun in any closed pipe, again just drill a hole in the end and any old percussion cap (or the trigger for a 'party popper') widely available at many toy-stores will work just fine as a firing mechanism.
3. Repeated use of many over the counter medicines can be extremely fatal, and not necessarily in horrible ways depending on how they function. For example if you huff loads of albuterol for an extended period you will almost certainly die of heart failure. A lot of people with COPD/COAD go like this without even realising it (doesn't hurt that they're already prone to heart failure, but that just quickens the process) you probably won't even see the heart attack coming and unless a doctor is regularly taking blood samples and checking your potassium levels whose to stop it? You don't need a prescription to buy the stuff and chemists don't track sales so even if you're going through a bottle a day no one will be the wiser. If you live alone the odds you'll be resuscitated are pretty nonexistent. It's probably not a bad option if you don't want to have to work up the guts to 'pull the trigger,' on something final.
4. Electrocution, you want to ground the current through your heart. You could even set it on a timer after knocking yourself out with a huge amount of benzos. Painful but a hell of a lot more fatal than some methods people pick especially if you just grab a live wire with both hands since it will be physically impossible to let go until you're meat. This is also a potentially workable option for people who are being monitored and have limited privacy. You need an extension cord, a box-cutter and about ten minutes, though it may not be feasible in some locations depending on the frequency/amperage and volts of a common outlet, but with a little research you could do the same with your home fusebox (especially if you hook yourself up to the current before it runs through any safety switches, not that any of this is likely to trigger one to my knowledge as they generally trigger as a result of surges, such as when something live is dropped/thrown in water) and even in some countries with low power outlets many products, like microwaves, use transformers that are more than up to delivering a fatal shock, but that requires a lot of tinkering, or you can just buy a step-up transformer online and hook that up to a stripped cord, or even use a generator (you can hire them fairly inexpensively) if - for whatever reason - you do want to do the old 'live current in the bath,' thing which is about as fatal as it gets, but at least it's quick.
6. Also unpleasant, but if you smoke enough cigarettes in a short enough period you're a dead duck. Though when I say you need to smoke a lot I mean a hell of a lot. Probably not feasible if you're not a practised chain-smoker already.
7. Poisonous mushrooms are pretty widely available. Death caps don't have that name for fun, and although amatoxins are
the definition of slow and horrible the one upshot is the process is almost
totally irreversible. Some are even tasty and most retain full toxicity even after cooking so you don't even have to force yourself to eat something nasty. The main reason I'd consider this though is it would allow you to spend your last hours surrounded by friends and family (assuming you have them) and with access to top-of-the-line palliative care (morphine on-demand doesn't sound so bad for example) since the odds of a hospital being able to do a damn thing are very bloody close to zero if you wait four or five hours before calling them (pain isn't going to set in yet) and they don't happens to have a spare liver on ice, which is pretty bloody unlikely.
8. For the really desperate; drink a half a glass of isopropyl alcohol. Not pleasant, but dirt cheap and widely available. Also easy to do stealthily if people won't let go go any other way. Ironically some psyche wards even have the stuff lying around if they do art classes. Since 'artists alcohol,' is about 97% pure isopropyl.