First things first, try a different med. Sertraline is always the first one offered usually followed by Citalopram as they are the most widely tolerated and quite versatile. They are not the only option. Try a few alternatives. If You have no respiratory or heart problems I would ask your GP about trying Propranolol which will only treat the physical symptoms of anxiety but will at least get rid of that sick sense of dread.
Secondly counselling is great and I personally have found it an invaluable support but it isn't always the answer. I've heard very good things about EMDR therapy for PTSD. In my personal opinion mindfulness is bullshit. Its fine for a bit of mild anxiety and depression but for PTSD level anxiety, it's like trying to fix a burst pipe with plasticine. Look into a few different types of therapy that could help you, interview a few therapists to find one you can really work with.
Thirdly, nothing I've suggested will make a blind bit of difference in the longer term if you don't get out of that toxic workplace. Take it from someone who has been there, a year down the line you will be wondering why the hell you didn't tell them to stuff it sooner.
From what you've said about them questioning your performance they could well sack you soon anyway. Is one or two or three more months pay worth the toll its taking on your mental health? It wasn't for me. I wish I'd told them to shove it up their arses and fuck themselves with vigour.
Apply for anything. Even out of your field. Even if it means spending 8 hours a day doing mind numbing data entry tasks. Sign on with agencies for temping work if you have relevant experience. Even if you end up working two jobs at once you'll still be happier than you are now. Being bullied drains you in a way people can't understand unless they've felt it. Trying to keep up that professional front while they chip away at you is exhausting, I know. I've been there, going steadily downhill yet refusing to quit in case of financial disaster even though it was making me suicidal with unhappiness and my desperately worried therapist trying to prop me up emotionally and taking my calls at ridiculous times of the night, practically begging me to just quit. He even offered to see me for free if I couldn't find another job and you know what? I ended up getting sacked anyway for 'not really fitting in.' Looking back, God knows what I was thinking. My therapist was right. No job is worth your mental health. I was crazy to stay.
Is there any possible way to absorb the drop in pay? It doesn't have to be permanent. Just enough to give you some wiggle room to get back on your feet.