When do you know you've had enough?????

Is it when your effort isn't anywhere near 100%? Is it when you dread doing something that you previously loved to do? Is it when the smallest task seem so monumental? Is it when just the sight makes you visibly upset? Is it when that pep in your step has become a slight but steady drag???

Or Is it that you don't have or notice any of the symptoms above....because you've become so numb that you don't have any feelings at all.