Whew.........this is a toughie.
To be honest, I'm more concerned that you may be overreaching now that you're feeling better. I've done it countless times myself---and very recently too---and I always wind up getting knocked flat on my assets, either because I run out of enthusiasm or get in over my head. You, being new to the bipolar diagnosis, are even more at risk because you're still working to achieve long-lasting stability and you just don't have enough time in yet.
FWIW, it's taken me over a year to reach anything even remotely close to stability, and now I'm fighting another setback because I overreached and took on too many projects at work. We're under the gun because of a bad survey and can't seem to get unstuck---we had our second re-visit this past week and failed miserably---and my director and I have been notified that we will be fired if we don't pass on the next re-visit.
So essentially, I've been busting my rear for NOTHING, and I am angry and upset and severely
anxious. I'm coping better than I used to---I haven't flipped my cork---but I'm also on four different meds for my bipolar disorder. The thing is, extra stress tends to destabilize people with our illness, and in all honesty, I think you probably ought to consider passing on this promotion until you've been OK for at least six months to a year.
As for discussing your condition with your boss and co-workers, I wouldn't do it if you can possibly avoid it, unless you need special accommodations in order to do your job. (I do need them, so my company is altogether TOO familiar with my mental health issues.)
Wishing you the best of luck, whatever you decide to do.