Get your Union involved prior to going into the meeting. This way they can get prepared for whatever might happen. Don't let your supervisors bully you into anything.
If your suffering from depression this is another reason to have your Union steward with you at this meeting. This way you'll have someone else in your corner for moral support.
I know from another thread that you have a government job. I used to also so, I know what kind of games can get played by management. If your supervisors are anything like mine were they may be unique but, they aren't uniquely qualified for there position. Good luck? I'll say a prayer for you.