I hope this doesn't sound overly simplistic, but it has changed my life. I have struggled with anxiety and depression for most of my life. A couple of years ago, a therapist said, "Have you tried thinking of something else?" when I was explaining running through anxiety-inducing scenarios in my head.
So now when something that causes anxiety or dread starts to show up in my head, I immediately say "I don't want to think about that" and I say a little prayer. Sometimes, I keep repeating the prayer to keep my mind occupied on something besides dread.