Sorry to hear this Marty.
Not a lot I can add as there is already a load of good advice posted previously.
Been in this situation myself a few years back. Three month review was excellent, no problems. However job I was working on started to go to sh*t (not my fault at all) but my manager (who was at fault for a lot of issues but was too busy climbing the greasy corporate pole) needed someone to pin it on to save his own ar*e......me.
Things came to a head when he asked me to grab a coffee and have a chat through the job......instead he started to pull me, my work, management capabilities apart. C*nt - time to get out.
So, couple of interviews later was offered another job fairly quickly - wasn't ideal, but needed to jump before being pushed.
Wrote a nice email to HR informing them of my mental health problems and how this had triggered things and ...nothing (HR were useless). Doctor's note for a week which didn't go down well. Fate sealed.
I knew I had something sorted, but was waiting, waiting for the formal offer to come through....tooke a while.
So, was called to my 6 month appraisal with my boss......and HR. So, walked in knowing full well this was either going to be the start of disciplinary procedures, or formal notice. So when they started I just said "can I stop you there, I've got another job, I'm leaving, I'll formally hand my notice in now. Thanks" and walked out of the meeting. Look of complete disbelief on both of their faces was lovely.
If I see my old boss again it's going to be very difficult not to f*cking smack him one, the slimy c*nt.
So anyhow, stay strong, you will get out of this s***y situation - but use every trick you can - mental health, doctors notes, raise formal grievance etc to buy some time. Do everything you can to sort yourself out.