Sounds like what happened to me. I've always been depressed, always, though at times I did have periods of doing the whole "yeah look at me talking to people, thinking positivie and doing things!" which I guess is mania. I have no official dx for being bipolar but my mom does and I wouldn't be surprised if I'm just undxd.

About a month or so ago, I started getting reaaaaally depressed, I was watching some old music videos and suddenly I remembered my grandparents (I get a lot of flashbacks to childhood when anything from 2003 and earlier plays) and finally the emotions I was blocking of them came flooding and I finally started grieving after being numb for years. Then I got more depressed about life in general and felt like I was sort of losing my ability to go into manic mode because I feel more and more that those thoughts I feel then are bullshit and temporary so why even try?

I had a prescription of Wellbutrin lying around so I decided to try taking it again but it made my nose run CONSTANTLY and at the time I worked at a chicken plant and that side effect was simply intolerable with that job. I quit cold turkey, didn't want to because it made me really calm, but at the same time it made me move my suicide plans from someday to that month or week. After that, I began thinking of how much of a retarded, weird, asshole I was (not in my head either, it's true) and how much strange and terrible behavior they've seen from me and then I realized people were looking at me with such albeit understandable hate, and contempt so after 3 days of my bubble getting smaller and avoiding more and more people each day, I quit and I am now working on mturk and avoiding the phone and haven't opened my mail since I quit. I don't want to do ANYTHING. I don't want to even get better, I want to just not exist. That'll never change.