You sound kind of… mentally overloaded to me, though that's not exactly a diagnosis and I'm hardly an expert, just another human being who's also had mental health struggles. But it makes sense to me that when we get overloaded, things shut off — like you say, you've had enough!
Hopefully if you can get your folate/ferritin under better control, and the sertraline starts kicking in, your mind will be better able to sort through all the stuff that's been thrown at it. Grounding techniques for anxiety and dissociation might help in the meantime — I find holding and focussing on a heavy object good for bringing me back into myself and into the moment, but you might find something else more useful, like focussing on all the different sounds you can hear, or making and drinking a hot drink while paying attention to all the sounds, sensations and flavours, or whatever you find works best for you when you're feeling detached and zoning out.
If the anxiety keeps on being worse than it was before, then it might be that sertraline isn't the right medication for you, but if you can give it a chance first, it might end up being helpful for you — the side effects you get can be different at different doses, and often decrease after the difficult initiation period.
I second Emily's point about a therapy referral — sometimes local NHS talking therapies services offer self-referral, if that's easier for you than going through the GP, though they will inform the GP that you've referred yourself.