Can you take a leave of absence? I know it's risky (I recently lost my job after returning from a LOA due to a bipolar episode) but it may be your only option at this point.

Your mental health is much more important than work, if you get right down to where the cheese binds. I know how you feel about work being a large part of your identity---that's what I struggle with the most now that I have no job---but again, if you don't have your mental health, you've got nothing.