Same here. I also found that often there's not any cause in the sense of something specific upsetting me; it's just an automatic reaction to not getting enough social interaction.

Well I don't mean ruminating about the cause of the sad feeling. That is probably one of the worst things you can do. Rather I meant just identifying it.

For example, when a girlfriend and I broke up (this was a couple years ago) I spent maybe two days feeling really depressed. Eventually, I thought to myself, "You're sad because you broke up with your girlfriend."

That really put it in perspective for me. It made me think of all the cheesy teen movies where kids breakup with their sweethearts and act like it's the end of the world, when in the viewer sees it as a normal, even banal rite of passage to adulthood. I had always thought people who reacted like that were ridiculous. In other words, it feels like that thought put the issue in "far mode" for me.