To ask for advice about work? Sick leave? I don’t know what to do

[MoralHighGroundGrandWizard]

Work is horrible. My manager is awful, bullying, aggressive. (She times lunch breaks of staff I manage, has stood over everyone shouting “I AM THE MANAGER OF THIS OFFICE YOU WILL DO AS I SAY”). I am the assistant manager. It is a high pressure job but not amazingly paid (NHS). I have been there 6 months. I found out the previous person in the job left because of the behaviour of the manager. She raised it with higher ups, it’s gone no where. I have raised the behaviour, nothing. I think my manager has actually put in a grievance against higher ups so they’re scared to go near her. It’s a nightmare. Of the 3 people who share an office with her, all of us are looking for other jobs.
I have got a secondment in the same position and same pay in another office just to get away (my predecessor also did a sideways move to get away in the same hospital). It is for a year. I got this a week ago and she has been even worse since I told her. she told me she no longer trusts me, is disappointed in me, and that I will start to see the “real” her. She has also told me I am no longer allowed to work remotely 1 day per week. I have raised this with HR and the higher manager who disagree with her but have told me I need to have that discussion with her.
I had today off annual leave and the dread and anxiety I have of returning to work tomorrow is crippling me right now. I am not sleeping well, because of thoughts of work and her behaviour and attitude. I just don’t know what to do. Everything is screaming at me to ring in sick, but also that might just make her behaviour worse.
does anyone have any advice? Walking away from her she follows you and shouts at you. Then you have to go back. I’ve raised it as high as I can, through every avenue I can (HR, management, Chief exec) and NOTHING happens.

You can't "sue for constructive dismissal" unless you leave...

So an update; I struggled through another week then yesterday I couldn’t get out of bed for most of the day. It was like I was catatonic. I barely spoke. I barely moved. I woke up at 4 this morning and just couldn’t do it. I turned off my alarm and went back to sleep until 8. I’ve texted my manager this morning and told her I wasn’t well and couldn’t come in. I’ve spoken to my GP who has signed me off for 2 weeks. Now I have anxiety about sending the sick note in! But I will, I’ll just email it.
I feel awful - so guilty and like it’s my fault and I’m being so over dramatic reacting like this.

You absolutely aren't being over dramatic OP! I had a problem with my boss at one place I worked at, I reported it to the owner of the business, but of course she listened to my bosses side, and sided with her, because it would have been harder to replace her than it would me, as I was only 'support staff'. I ended up getting a telling off from both of them, which I felt was totally unwarranted and humiliating. The whole situation had been building up for a long time, and when I left work that night, I'd reached my limit. I drove home, got through my front door, and then collapsed on the floor in the hall, where my DH found me some time later, still sobbing my heart out, as it all just seemed SO unfair! When he eventually managed to calm me down, he told me that no job, and no amount of money was worth my health and mental wellbeing, which was backed up by my elderly Mum, who's advice I trusted unquestioningly. So I went in the next morning and gave my notice. While all of this had been going on, I had of course been looking for another job, and having put my resignation letter on the bosses desk at 9.00am, I received a phone call at 9.10am, from an agency offering me a long term position that I'd interviewed for a week previously. I can't tell you how good I felt, but just having put my resignation letter on her desk, I felt like a 10 ton weight had been lifted off my shoulders, even if I didn't have a job to go to.

I think in your shoes, while off sick, I would write/email HR and tell them that you have been signed off for 2 weeks due to the stress you're under, from working with this woman who is bullying you. Point out that you have made complaints before, and lay out everything you have done to try to get the situation sorted out. Also point out that as 'PlanningTowns' said, 'your employer has a legal duty to ensure your well-being is protected. This includes from bullying', and tell them that they are failing to do this.

As I said previously, I have no experience of working for the NHS, but this simply cannot be allowed to continue, so again, I would urge you to follow 'PlanningTowns' advice, as it sounds like she knows what she's talking about. Maybe even private message her, and have a proper chat about what she knows, and what you can do. Please don't let this woman get away with ruining your career for you.