It's definitely not as simple as just quitting your job, and people who are offering that probably don't fully understand your situation.

I think it's definitely one of those things that is a very delicate balance. Just quitting on a whim is never a good idea, especially if you haven't carefully considered your finances. On the other hand, you have to know at what point the damage to your mental health is too severe to continue and more damaging than the stress of finding a new job and managing finances without a job.

In my experience, it took a while to learn that just dropping everything when the stress is overwhelming and damaging isn't the best idea nor is staying at a job that's clearly damaging. The balance I found that worked the best was stay at my current position, but stay as emotionally detached as possible and only commit just enough energy to do the basics while focusing the rest of my energy into finding a better position. However, it's definitely easier to say than do.

From everything I've read, you're an extremely hard and dedicated worker which is usually an excellent trait. However, in this case, it might benefit you to step back a little bit and pour a bit less into work and more into your self-care. You seem to consistently go above and beyond, which I respect, but when you feel like you're in the right place, you should consider diverting some of that energy into looking for a new position.

Even if you feel that you're unstable right now, there's no harm doing some of the groundwork for looking for a new position, especially if this job keeps causing you enough stress to prevent you from stabilizing yourself. You don't have to dive into interviewing for another position right away; start with looking at what companies there are hiring for the same position you're currently in as well as companies in the same field with openings in their staff and learning what the application process is.

Most of the time, companies are pretty understanding when hiring for professional long term positions because it's a lengthy process and they usually prefer hiring someone who's looking from a similar position over people with the right skills who are currently unemployed.