You don't have to disclose anything---in my workplace they gave us a disability form to sign if we had what we considered to be a disability but there is nothing that says you have to consider your mental illness in any way a disability---there were guidelines as to what qualified. This was actually put in place to assist people with any accommodations they might require and not to single them out. In my case I work for the same person I did when I got sick we just moved locations so I had to be rehired by a different place. Also in my case my boss was among those who arranged help for me when I got sick(psychotic break) and not only does she know but she had to ask the chief of medicine for advice on who to contact to get me help. Even here her husband is the highest ranking medical official at the hospital and he knows just because it was part of her life. So I didn't have much choice in whether to disclose or not because everyone already knew and was very supportive as they would be for any illness. However I realize this is not always the case and I would not disclose it if I were starting fresh.

I don't believe there are any laws regarding disclosure but you would be protected under the americans with disabilities act if your MI is severe enough to be considered a disability. If the meds are working its probably not considered a disability.