Although I think the stigma for many mental illnesses in the US is much less than the past, it definitely still is a problem. Yet, I sometimes wonder if we fear repercussions more than anything, at least in some settings. I work for a local gov, so my employment is secure and my benefits are good with safe long-term leave time for medical reasons. I had my first real manic episode and was diagnosed (finally) about two years ago. I didn't have to disclose, but I told my boss because I needed a couple months off and he is a genuinely nice man, not to mention I had bipolar blabber mouth. ;) He was great about it. I just transferred to a different dept and also had a med change that left me with a lot of cognitive dulling for a bit. Unfortunately, I met with my new boss in the middle of it. I later chose to tell him I had a seizure disorder instead of bipolar. There is less stigma and it was sort of honest because I have had a neurologist say that I may have been having simple partial seizures most of my life. However, they are not why I'm on meds and may need allowances at work. So, even in a "safe" place to tell, I am very reluctant. I've just heard too many side comments about mental illness to willingly chance hurting my credibility and future career growth.
Otherwise, my family and friends know. I don't share with those that aren't close.
As to the different treatment by medical staff, I have experienced it w/one doc so far. What an ***. My appt was a waste of time. The terrible lesson is to not share with medical personnel unless they may be prescribing meds, and even then I'm apprehensive. I can drug check online and confirm w/my psychiatrist that there are not interactions. That sucks. My dentist doesn't know for this reason. I'll take the risk because it's not really his business.