Worrying is nothing more than a bad habit. We say it's a mood or an emotion, but it's really not. Like other habits, it serves a purpose in moderation. If we have a short-term spate of worry over something we can change, like having a difficult but necessary conversation with a co-worker, it serves the purpose because taking action alleviates it. But the long-term, obsessive kind really just a drug of choice. It gives us something to do so we can avoid pain, boredom and fear.
Part of it is puritanical in nature--we really aren't allowed to be happy unless we suffer, right? So worrying gives us the pretense of suffering, so don't feel so bad about being good. (Bloody Calvinists.) But more importantly, when we worry about something, we can confuse it with doing something about it. Except we're not doing a damn thing. We're using worry to avoid doing it, because the thing we're avoiding is too scary or difficult or just no fun. Right now I am worrying about packing rather than actually going through that extra closet where I've thrown junk, because that's going to be tedious and I'll find wedding albums and other reminders of failure.
And then there is good, old-fashioned, co-dependent worry. We obsess over finding just the right thing to make that other person give us what we need. If I look pretty enough and keep a perfect house and make sure the kids are taken care of, he'll appreciate me. If I make varsity and the Honor Roll, Mom will give up her four martinis a day and actually talk to me. Women's magazines are expert at exploiting this: "Get a Perfect Butt." "10 Moves to Drive Him Wild." So we worry about cellulite or technique because we think those things determine our lovableness, instead of figuring out why we don't feel lovable in the first place. That is hard and it's work no one else can do for us, no matter how much we pay them. It's less painful just to keep dancing as fast as we can.
When I get into a worry rut--this is usually between 3 and 4 am--I try to remind myself that if worry is a habit, I can break it. But my 3 am self is often quite unreasonable, so often I have to get stern with her and tell her to shut up and go back to sleep, because there's nothing she can do about it right now. And sometimes it actually works.