The amazing thing about humans, is that we evolved an ability to hold on to the concept of some abstract reward in the future.
This spurs people to do great work. We can very easily imagine a future where we are much more well-off compared to our present, and thus feel compelled to chase that future.
However, with evolution, comes mutation; we can just as easily imagine a future where we are much worse-off, and thus compulsively work to prevent that future.
The fact is, that this is true. Taking a break hurts us in the short term, while working harder often leads to better results until the eventual burn-out.
So the question should be: Do I need to put by best foot forward right now? And in asking that, realising that you're going to be trading a mountain amount of effort for a couple ounces of result.
As with everything, look to those around you for guidance. Some people have built great business and while their family crumbled, others with their family united. Some athletes have worked themselves to the podium, others to the hospital (and some to both).
The final question we need to ask is: What is my Philosophy? For a life with any Philosophy is bound to be more fulfilling than a life without; it allows you to define your version of winning.
And with that, I wish you a Merry Christmas.
 Of course, it is my consistent contention that we as humans cannot intuitively comprehend just how many losers there are, making us fallible to the notion that we're going to be the exception to the rule.