Replace "launching a startup" with any other variable and the answer will be the same.

What does it profit you to successfully launch a startup and not be able to enjoy the "spoils of war" or, worse, to have to spend your spoils on medical bills? Similar to the check engine and other lights that come on in a vehicle, health problems are the warning signs that a part of the body is malfunctioning. To ignore those signs and keep driving (regardless of where you are in the startup process) is to put yourself, passengers and other drivers at risk. Follow the owner's manual and go in for service as prescribed, i.e., get the appropriate rest and relaxation, eat well, exercise, etc.

If life expectancy averages remain the same, your body has to last well past your startup into your 70s and 80s. When you burn out early, you short-circuit the agility needed for your later years. It doesn't help that metabolism decreases as you get older so if you don't make time for exercise, good eating and rest now, your body will ignore you later ...