What can I do about a stressful work environment that is impacting my mental health condition?

I am a manager in a high stress call center environment. I have had my position in management for almost two years and about 3 months ago I was moved to a sales team based on my track record of being a top performer. I have suffered from bipolar disorder for about 10 years and for the last 5 years I have been able to cope with stress and mood fluctuations without meds.
Since moving to the sales area I have been bombarded with negativity basically my boss and his boss telling me that my performance is unacceptable and that they have no problem replacing my job. In addition to this I have had a lot of stress at home finding out my son is autistic. All of the stress is building up and has sent me into a deep depression which is preventing me from being able to be effective at work.
I made an appointment with a therapist to see if I can get a prescription to help regulate my moods but my concern now is that I am going to lose my job. I have never told any of my superiors about my bipolar because of the stigma attached and my fear of being passed over for promotions because of it. What can I do now to save my job without damaging my reputation at my job and save my sanity? Is a leave of absence something I should consider and if so how do I go about bringing that up with a new doctor?