You post strikes a chord with me. I have found over time that I personally require some mental challenge and some physical challenge to remain mentally healthy. Some days, work provides the mental challenge, the feeling you get by solving difficult problems. If we get too far into the weeds and end up in a constant state of talking about work instead of doing it, things begin to turn depressing until I need to supplement on the side by learning something new or whatever. Same goes physically for me, I keep pretty regular on working out but if I take a week or two off I start feeling sort of sad. Best of luck to you wherever you land!