Hey OP,
I was (am) in your shoes a few years ago. Like you, I first realised how bad it was when off on leave and I didn’t ‘bounce back’. You are a smart woman - I bet you have already tried lots of things on your own that didn’t work before you got to this point of being signed off. Now it’s hit home it is bigger than what you know how to cope with, so you are researching - I also bet you’ve already googled how to cope with this and asked people how to cope with it. Asking on Mumsnet is another way. All ways of trying to find out how you can keep going and doing the impossible.
It helped when I started to think of it like a DV relationship. Lots of women go back to toxic/violent relationships because they think THEY can act different and he will change. Or he’s made promises now, it will be different. It can’t and it won’t. You and your job are the same.
I also couldn’t quit immediately. I wanted to leave on my own terms, for a job I wanted (same pay/promotion). It was important to me. Although looking back, I’m not sure it should have been.
I immediately began looking for other jobs. I had a list of what I wanted and also a list of what I didn’t want, but would accept if the job hunt went longer than x time.
I also did the following things - NOT as a solution, but as a desperate stop gap to keep me on the rails until I got the new job.
-nutrition excellent. All fresh foods, healthy, no sugar, no coffee, no alcohol.
-exercise. Started gently with a yoga class doing only what I could do, and slow walks in nature on weekends. Movement everyday, but slow.
-sleep. I was in bed by 9pm every night, even if I couldn’t sleep. Good sleep hygiene, now screens etc.
-said No to almost every invitation. I needed every bit of time outside work to rest and recover.
-tried to put in boundaries at work. Firstly, that I would not check emails when not at work. Mobile only in an Emergency. Training people to respect that.
-saw a Dr to monitor my physical health. This was impacting my blood pressure.
-saw a psychologist.
The above got me through to a new job. But I don’t recommend it as a way of life. You lose your friends, family, everything to just survive for your job. I felt like a machine with work taking all my living hours and I would ‘power down’ for the next session.
Dont use the above as a way to survive the job. Use it as a way to get through less than 12 months to the next (better) job.
As otherwise you’ll be on here in 12 months, worse. And this time you’ll have to stop work, either via a heart attack or that you mentally breakdown.
Goodluck