Ohhh Sally, I'm so sorry to hear that. I know that awful dark place you are talking about. I've been suffering from depression for 21 years now and on antidepressants for that long. Sometimes I worry about the long term effects on my body and other times I just to say "oh well, gotta have them."--bad genetics plus life events.
You are smart to nip it in the bud. Go to your GP and tell him/her what's going on. You've been with it so long, like me, that you know the warning signs. I discovered after the MS diagnosis that depression is far more common among MS-ers than any other autoimmune disorder. Blech.
I've been fighting it lately too. Don't think what I'm on is working anymore my doc said there is a new drug called Viibryd (I think that's the name). As soon as I recover from collapsed lung I'm on it! I'm hoping it will make things better.
And as everyone said, the issue with your daughter is a major life event--those kinds of outside stressors can sometimes tip you over--I'm not surprised the depression is rearing its ugly head. So don't beat yourself up! Take care of yourself, be nice to yourself by going to a doctor soon for reassessment. We dont want you slipping any further as you know the deeper the slide the longer it takes to get back out. Hope you feel better soon.