Hi @Ilovehiking.
There has been some good advice given but I thought I would add my experiences to the mix.
I'm a high school teacher too. Last year I had a term off when I became unwell and decided to go straight back into a full load, though without the year coordinator role I had been doing (like you with many extra hours, no extra pay and no time consideration). It was a mistake and I struggled for a year with little support (I'm now having more time off). The school system, especially high school, is not set up for part-time work or alternative roles that have less contact time with students. It is a shame because those would be really great options to help ease the workload and the stress. I should have accepted the offer of a graduated return to work (I was stupidly too proud) and before you go back I would see if your school will support this. It may only need to be for a few weeks, but might take some pressure off. Can you also resign from your extra role, or ask for someone to take over for a while? Lots of people are looking for experience so they might be able to do it for a while with you as a mentor and you can decide if you want to go back to it or are better off without that extra workload.
Being a teacher is hard and as a high school teacher you may have 120-150 students, who all need individual care, attention and support. The expectations from parents, students and administraion is ridiculously high. If you are not feeling 100% then this can be overwhelming - this is not good for you and not good for the students. If you can manage some more time off it might be a good idea. A fresh start in 2018 may be helpful.
I have also noted how many teachers are on here - it doesn't surprise me but it does make me think about our education system and what the system could do to support teachers more. Happy teachers make happy students.