I can relate to that. I used to work not more than it was required for being perceived as a very productive person (10-15 hours / week), but at some point I couldn't stand it. I co-founded a startup and for first two years I easily crossed 60 hours/week on average, yet I was much happier and had more energy than previously. Of course 60 hours work week is not sustainable, but I definitely felt better mentally doing too much rather than too little.