I do logic puzzles.(
https://www.logic-puzzles.org ) I still have my old calculus book and I work a few problems out of it now and then for a change. I find focusing my mind deeply on something pushes everything else out of my brain and calms me down. I can still think when doing physical exercise - that doesn't help me.
Coming here to PPOT helps too. It's the most social interaction I get since I retired.