This is also why any list of insomnia tips say if you can't sleep, get up and go do something repetitive and boring. If you do all of your anxious thinking in bed, that becomes your habit -- you train yourself to do it. I say you need to train yourself to do it at some other time during the day. Force the issue; think of it as a body necessity, like brushing your teeth.
"So, what, you're talking about meditation?"
Holy shit, no. I mean, you can do that if you want, I've heard it's a good method. But any time someone recommends I take a ten-day meditation retreat to relieve my stress it makes me imagine myself whipping them across the face with a blackjack (which maybe is proof that I need it?). No, I didn't want to suggest meditation or yoga or any other hippie bullshit because this isn't about channeling your energies or listening to your soul -- it's just brain biology. I don't care what you do during your quiet time, as long as it doesn't involve new information coming into your skull. I know at least one person who goes into his back yard for an hour and hits an old tractor tire with a sledgehammer over and over.
This is why you've probably had more than one great idea in the shower. All of the necessary ingredients are there at shower time: no human interaction, a simple task, the only sound a steady white noise. Unless you're reading this from, like, prison, or something.
"But I'm the type to cycle endlessly over the same, useless thought! I've been beating myself up over dumb shit I said when I was 12!"
Me, too. Have you tried writing it down? Or telling a stranger about it (a counselor, or ... somebody)? See, the reason the brain repeats memories or worries over and over is probably because it's afraid you won't remember it long-term otherwise. This is why another common insomnia tip is to write down what's upsetting you every night, even if it's just a to-do list of the unpleasant stuff you have to do tomorrow. It's saying to your brain, "Okay, this data has been safely stored off-site, you can stop replaying it every ten seconds, you freak."
Do you remember Arya having any insomnia subplots on Game Of Thrones? No? Exactly.
I also think this is the primary benefit of therapy -- you're still stopping your day/week to think through the stuff you don't normally have time for, only with the help of somebody who can make sure those thoughts are actually productive (which is probably better for our hypothetical guy who at 30 can't get over that time he peed his pants on stage during a high-school performance of South Pacific).