I had to do that with what will probably be my final pharmacy job. I worked at a very good small hospital with some of the nicest people you could ever meet......and the job was literally killing me. I had been in the ER because of the stress and lost about 15 pounds in less than a month, and realized that if I worked there one more day, I would be a patient IN that hospital. The job itself was just plain old that stressful.
I should have known something was wrong when I found out it took 4 months to fill the job, what with saturation and all. I don't know how the other pharmacists, who unlike me also had families, coped with it.
It was one of the hardest, most wrenching decisions I've ever made, and I'll never forget the look on my manager's face as he handed me his card; he looked like someone had just told him a close relative had died.
If you look up "quitting a job without notice", one of the justified reasons for doing so is "Your physical and/or mental health is in immediate jeopardy" and that was definitely true for me.