Welcome to PC! So sorry you're going through this. I know how it feels, as it's happened to me too (although my boss actually comp'ed me for the mental-health days I took instead of making me use my vacation days). I had a pretty serious hypo/manic episode last summer that ended in my becoming hostile, verbally combative and just an all-around pain in the arse, so I was ordered to go home until I could get stabilized.

Fortunately I was able to get on some meds that brought me down quickly, and all was well.....but that episode really let the aforementioned cat out of the bag as far as having bipolar was concerned. I'm very fortunate that my employer is understanding, but if I'd had a choice I'd rather not have had to disclose my illness.

As far as your employer needs to know, you have only a "medical condition" that flares up every now and again, and requires rest when you're ill. (That's what my pdoc told me to tell my boss when the question of working a few night shifts came up recently. I am basically forbidden to do so because of my bipolar, but I don't want to make a federal case out of it.) There is no need for them to know details about your health history.....like you said, if a diabetic employee says they're feeling bad because of blood-sugar variations, nobody even raises an eyebrow.