I find that very often the perfect cure for too much "thinking" work is an awful lot of physical work. I started feeling a lot better about working on my Ph.D. when I got a second job stocking shelves on the night shift.
If it wasn't for Brazilian Jiu-Jitsu and lifting, I would be lost.
Training BJJ and MMA is physical, skill-based and social. I train with people who don't care if I miss or make the next paper deadline. They only care that I show up, work hard, and be friendly. Lifting by myself has a meditative quality.
Most people go through a week without ever exposing themselves to real physical exertion, and I have no idea how they cope.