Sleep is such an important piece of the puzzle. Sadly lots of doctors and clinicians don’t spend much time on that but it does have so many other effects!
Another big one is your lymphatic system. If the person isn’t moving around their body enough their lymphatic system can be clogged and lead to all kinds of health issues, with a lot of mental state changes being a common factor! There’s a great podcast that talks about it - Stop Chasing Pain. He did a mental state lymphatic episode a few weeks ago it was really interesting!