It must have been a while since you were here, because I don't think we've met, so to speak.
I'm sorry things are building up like this. I could try and give you a load of advice about dealing with your employer, but to be honest you do sound stable enough at the moment to deal with them effectively if they were playing fair, so it's not going to help.
A couple of things I would suggest are to write a letter of grievance to your employer about the lack of information and working conditions (in case you end up at a tribunal, you'd have something on file), and if you have a good GP, visit him/her and get them to give you a bit of time to collect yourself, that is assuming you get occupational sick pay.
As for depression, I wish I knew how to stop it, because I'd cure everyone on this board. If you're still able to enjoy things, don't let this situation put you off, especially on a sunday. It's important to have good stuff in your life as well, particularly when the rest of it isn't going so good.
I hope things improve soon.
5/11/12 1800, Trafalgar Square: re-enactment of final scene from "V for Vendetta" Be there.