Thank you for writing this - this lesson can be life saving. I learned this lesson the hard way, recently losing a friend and mentor to suicide. He was a brilliant entrepreneur but hit a road block post-series A where he couldn't raise follow on funding and the press started turning against him. The business was his life, and he wasn't able to separate himself from the business nor did he have a life outside work with the kind of wins which can sustain through these challenges.

Exercise helps, but I'd reinforce the need for a balanced supportive social network outside that. Choose sports with other participants (eg racquet sports, or join a team). Not only will the discipline of not letting others down keep you motiviated to keep going, but you'll get friends who don't give a damn about your business (in a good way - no need to pretend to be killing it all the time!) and can keep you grounded in normal reality.