Hamster Wheel Brain
When your brain runs about some issue over and over again and won't stop, just like a hamster running in its exercise wheel. It keeps running, but doesn't get anywhere.
I'm having such hamster wheel brain about whether or not to take this job offer.
hamster-wheel brain
an instance of one's mind going over and over an issue or problem without finding a solution
I had a major case hamster-wheel brain today. I could not get organized and could not stop thinking about it.