I've never really emerged from the other side of Depression and like yourself my mother also had it although she has managed to come out the other side mostly. Fun times though sitting up with your mum untill 2 am to make sure she doesn't do anything stupid.
I'm certainly not bi-polar or even clinical but I've always found Depression hits people in different ways over different things. I just eventually learnt to shut myself off, for the most part with the help of alcohol, figuring if I didn't care about something or anything, the state of things, be it the world, or events in my life, couldn't get me down. To a point I was correct, although every so often I'll see or read something and that'll set me off.
What I did learn is that whinning about it never helps, it may help you, but after a while people get tired of you going on about stuff like an emo, even though they will listen out of politeness. So yeah, my way of coping was to essentially cut myself off from caring about people or myself lol.
It hasn't turned me into a very nice person, but it works.
Edit: Whilst I was typing this several people brought up Suicide. I've been there, at the top of builings, near railways lines, and I've felt that urge to just let go and not have to worry anymore but I do not condone Suicide. A part of me, maybe the stronger part of me, considers it weak and shameful which is why I never went through with it. Only you as an individual can ever truely know your mind though, however advice for when you're feeling like pulling the trigger, don't think in the moment. At that moment everything is telling you to do it, you don't think of anything you will miss or anything you'll care about, pull yourself back for a second and really think.
