When I start to fall into a period of depression, I withdraw from the world; I don't go out, I don't talk to people, I feel miserable doing anything. How do I

When I start to fall into a period of depression, I withdraw from the world; I don't go out, I don't talk to people, I feel miserable doing anything. How do I counter it? By forcing myself to talk to people, by working on something (it doesn't matter what -- if you don't write 1 line of code, you won't write 10), by going and doing something fun with a friend (e.g. watching a movie). It's hard, it sucks, but it typically works decently.