What are your depression triggers? (I suppose I should put a trigger warning here to be safe...)

I can figure out my hypo/mania triggers (sort of), but I cannot, for the life of me, figure out my depression triggers!

Obviously the loss of a person, loss of a friendship, loss of a sentimental item, etc. will trigger depression. (i.e., any kind of loss.) That's kind of obvious. But I'm looking for less obvious triggers because I've been getting lots of short depressive episodes that last 2-3 weeks and I'm sure at least some of them may be triggered?