The really irritating thing is I'm anxious about anything. I get anxious, and then I worry about how that anxiety will affect things, not the other way around.
I'm trying to up my b12, being super careful with what I'm eating, etc etc. Iron would be a good idea too. Getting out in the sunshine when it's out. November hit me hard this year, but now it's snowing and that's actually cheering me up a bit. But this is more than a seasonal thing.
I do also think that we're kind of prone to it. I was more or less fine for a few years and now, bam! Depression kind of runs in our family even though we don't really talk about it. We also (as a society) don't often talk about the fact that depression/anxiety isn't just about being sad/worried. It's an underlying tension that's there even when you're feeling ok. It's an instability. Today I'm doing ok, but I've got this slightly neurotic shakiness that makes me feel I could just break down at any moment. It's very unnerving.