Hi Nacht, Here I am just as I said I might be. Caught you here and cannot resist "jumping in". I suspect very strongly that the problem lays with your meds, especially if you have not been on them for some time. Maybe the pdoc started you on too high a dose. Ask him to lower it somewhat and see what happens.
I think you need to be in that concert in March. It would certainly add to your self-esteem. For me it would be a great morale booster. To pass it up, I am afraid you will be "kick-butting" yourself on the performance days. You cannot afford to feel failure when you are dealing with depression. It only makes it worse.
Try and think of this whole thing as a challenge, and then, put the boxing gloves on and become a winner.
I might give your concert master the benefit of the doubt. Just tell him only as much as he needs to hear. Do it in a strong positive way that will show him how much you want to remain with the choir. Let him make the decision. Right now you are assuming that all is lost. I don't think so.
You CAN conquer the "black dog" (depression)! If he is biting you, bite him back.