It seems to me like you need time/rest/space now, Babygrand - then you'll be in a better place to make any longer term choices. It's hard to make decisions when every ounce of energy is geared towards survival. You need respite now. Health has to come first. That's for your good and also for the good of your pupils. It sounds like your body is telling you that you can't keep going... it's best to listen now!
Do you have a half-term? If so, you could make the decision to stop straight away, and have three weeks to rest, with pupils only missing two lessons (which is nothing in the grand scheme of things, even for exam pupils). Even if you teach through half-term usually, they'll be used to other things stopping when the schools do, so it won't be a big deal. If it would take you ages to craft a suitable email to pupils (as it would me!), ask here and I'm confident you'd get a number of suggestions, one of which is sure to suit you. But it could be as simple as. 'Dear pupils, my apologies but I'm unable to teach this week due to illness. Please keep practising! Yours, Babygrand.' That could be followed up next week by 'Dear pupils, I'm afraid I'm still unable to teach this week. Have a lovely half-term holiday and I hope to see you after that.' That puts a plan in place, while also freeing you from actually committing to going back after half-term, and you can give yourself a good rest before even thinking about what you need to do long-term, whether that's a substantial period off work, or doing something different, or cutting down with pupils. We can help with what to say when you get to that point, so don't worry about that now (or anything else). Just rest.
Talk to your GP (and if they don't seem to understand or be able to help effectively, find another one) and talk to ISM. I'm not in ISM, but I'm in EPTA, and they'll send around emails with events/ adverts etc. If ISM do the same thing, you could ask if any teachers would like to take on some temporary pupils by Skype or something. Or they might suggest teachers who live in the region who do one-off coaching, which might be perfect for exam candidates.
I have a long-term condition which means I have to pace myself. Last year, I decided to reduce my teaching year from 39 weeks to 38. I went through the 'but will my pupils miss out?' questions, but ultimately, I know that they will suffer if I'm over-tired. I also know other teachers who have taken a few months off to travel, and almost all of their pupils either waited for them, or came back to them when they returned.