HOLD UP, BUBBLYBOO!
You may do permanent injury to your professional work history if you don't handle this properly. I know your principal seems like a jerk, but you probably need to take a deep breathe, and slow down for a minute. It sounds like you are in panic mode, so you're willing to do anything to get out of the situation.
This situation probably didn't become intolerable overnight, so handling it more slowly would be advantageous. You need to follow the proper procedures listed in your teaching contract, usually through human resources. If it takes a note from your doctor, emphasize the need for a break due to some unspecified stress, but don't have a "return to work" date included. That way, if the note goes into your personnel file, you won't be seen in a negative way.
If you just walk off the job, you are pretty much killing any chance you might have in the future for another teaching position. I know you may feel like you never want to teach again, but you may not feel that way a while down the road. Regardless, you don't want a black mark on your work history if you ever are ready to go back to work in any field. You never know if your references will be checked or not.
Good luck and let us know how you are doing.
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