This is a great opportunity for you to work on your mind's traits, especially equanimity. The situation is what it is; you have already recognized it, and have taken first steps to rectify it. So far so good.
From experience, I'd recommend this:
Take care of yourself
- Try to unclutter your life as much as possible. From your description I assume that your private life is non-existent anyways, or really fraught. If you have lots of stress in private life as well, e.g. because you try to get some hobbies etc. in, try to relax that as much as possible. The goal is not to reduce the time you spend in your private life even more, but to not fill it up with stuff you have no energy to do anyways, now. So that when you are off work, you get real relaxation time in.
- Use any time you have made free on focusing on eating well (cooking real food if you are at home), and sleeping as much as you humanly can. If there is any kind of exercise you could be doing, even just a few stretching exercises at home, try to do that, it's good for your body and alleviates stress.
- Get into meditation. Nothing mystical/religious, just plain old mindfulness meditation. Quick intro if you don't know anything about it yet:
- Sit still, close your eyes, and just be aware of what happens. You can sit however you want, on a chair, sofa, big cushion, whatever. Don't force yourself into a posture you see in YouTube videos which hurts your knees or leads to nerves falling asleep. If you need, you can move (i.e. if some joint starts hurting, move; or if you get an itch, you can scratch it).
- You do not need and should not try to reach any "goal" with this; for some people it is helpful to focus on your breath (i.e. on the feeling of the air cooling your nose or moving your breast or stomach), but this is not the "end goal". Just sit there, close your eyes, listen to whatever sounds there are, watch the darkness behind your eye lids, feel the feelings in your body (pressure, tingling, heat, cold etc.), be aware of how your emotions are doing (angry, frustrated, exhausted, happy, etc.), and if you notice that thoughts are appearing, just be aware of them.
- Do not try to actively influence any of that. I.e. do not try to make your emotions go away. Do not be angry when you catch yourself thinking about work, but gently be aware of it and witness how the current thought dissipates on its own. Even if the whole session feels totally futile, as long as you are sitting still and doing nothing, it will do something. There is not a goal of "emptying your mind", just to be aware of everything that's going on.
- Start out with 10 minutes daily and make it longer as you feel it's appropriate.
- There are some great apps or online resources for guided meditations like this; I don't know if it's allowed to mention these here, but if you're interested, add a comment and I can tell you what works for me.
Relax about the importance of your job
- Convince yourself that your job is not a life-and-death issue.
- If some manager tries to make you work faster, recognize that it's their problem, not yours. In the EU you are protected; your employee cannot bodily harm you or force you to do immoral etc. things.
- Remind yourself that those people giving you a hard time are also human beings. They are very likely overwhelmed just like everybody else, and the fact that they're in over their heads results in an overall abysmal behaviour. It's highly unlikely that anyone is doing it intentionally to cause harm for their co-workers. Have pity with them, not anger; don't assume they are stupid or evil.
- Your contract contains an hourly limit of how much you are obliged to work. Read up on that, and reduce your working hours. You are not interested in a career in that company, it doesn't matter if someone thinks badly about you.
- Obviously, if you don't have one yet, request an employer's reference ASAP. In at least my EU country you are entitled to get one every few years, no questions asked, and it cannot contain negative things that you are not OK with (i.e., they cannot write negative about you simply because you insist on working within your contractual hours).
Activate a maintainable working mode
- When going gets tough on the job, and you notice that your body is flooded with adrenaline, you're getting shaky, and just overburdened with stress, an immediate emergency activity is go to the bathroom (if you're in an office), sit on the throne, and do the breathing for 5 minutes. This stuff has measurable effect on stress levels; these 5 minutes will of course not change your problem, but it may calm down your body just a bit.
- If there are discussions (like you mentioned - managers 3 levels up arguing with you), keep everything as objective as possible. Try to never make it about people, but always about objective facts.
- You do not tell us which type of company you work in, but do try to establish some kind of activity/task tracking. Google "SCRUM", "Kanban", "Agile" - if you are in IT then you are aware of that stuff already. But a lot of the mindset behind it is very much applicable for any kind of work environment.
- Try to read up on these concepts and figure out whether any of it can at least somewhat be introduced at your job; even if only privately for yourself. Being able to cut your work into little pieces ("stories", "tasks" ...) and making them and their status visible is an awesome tool to reduce the overwhelming feeling of everything just being too much. Also it allows you to always be very aware of which one thing you are working on right now. You can also then make your work very transparent to colleagues and higher-ups.
- Use this to especially identify anything that can be prioritized away (even if you only use the old A, B, C, D scheme with the important/unimportant, urgent/non-urgent dimensions).
- If you find yourself in a heated discussion with people yelling, especially if they yell at you, then immediately perform some emergency maneuver. It's a little hard to give advice that fits your situation, as I know nothing about it, but some hints:
- If it's an online setting (video call), fake a technical issue (Alt-F4 on your chat app...), close your eyes and sit for 2 minutes before going online again.
- If it's a face-to-face situation, do not respond quickly to anything. Let them yell, and when they're done, let there develop an awkward silence. This gives them a chance to think about what they've said just now, and it gives you a chance to calm your thoughts and respond in a calm matter.
- Don't be afraid to respond with something like "I think it's a good idea to open the window for a minute to let fresh air in" (if face-to-face) or "I think we should have a short break, let me refresh myself and I'll brb" (if online); adapt as you see fit.
- If someone has you defend about some issue you had nothing to do with, just explain "I wasn't involved with this and do not know the details; let's get in Joe, he should be more knowledgeable about it".
If the burnout hits you
As far as I can tell, the light at the end of the tunnel is the oncoming train, in your current situation.
If the time comes, you will notice that it's over. If you start crying after a phone call and cannot help it, if you cannot sleep at all anymore, if you consciously feel that your body is a wreck and just flooded with adrenaline all day; if you feel that you are constantly in a state of panic and deathly fear; if you develop thoughts about killing yourself, then set an autoreply in your mail client, switch off the PC and the smartphone, head to your doctor, and be done with it.
Depending on where you are in the EU, certainly if it's in Germany, you can go to the emergency room in any hospital and just check yourself in. Tell them that you are burned out and are having concrete suicidal thoughts, and you will receive help. At this stage, this is a bodily issue, a concrete medical issue, not something "in your mind" to be ashamed off.