Causes: This habit is called "co-ruminating," says Amanda Rose, an associate professor of psychological science at the University of Missouri. She has found that while we expect that getting everything off our chest will make us feel better, that often isn't true. "We've seen that there's a snowball effect where talking about your problems causes you to dwell on them, and dwelling makes you feel depressed, which makes you complain even more," she says.
Treatment: Rose says the tricky part is that the problems we tend to rehash—relationship snafus, for instance—are inherently difficult to solve (you can't change other people). Resist unloading on your neighbor or the babysitter, and wait to share the story with someone you trust to give sane advice. Rose says that sometimes changing the topic will be enough to distract you (making conversation is good; it's overanalyzing problems with others that can get to you). Focus on other people's stories until you lose interest in your own.