When I was stuck in bed for 2 months straight in 2014 from a broken neck, I got a couple of Sudoku books and did every puzzle in the books. Now I just play Open Sudoku on my phone. Ever since then I kinda measure my pain/mental/overall sleep quality state by checking how fast I can solve the hardest puzzles that have real solutions without guessing. Anything over 5 minutes is bad for me.