How do you know when enough is enough?

When do you cross the line of working so much you drive yourself mad? I have 3 jobs (Barn help/horse loper, horse trainer, and Hardees employee), and I also board/train horses, and give riding lessons. I also attend school full time. This week I think I have crossed that line. I worked until at least 10:30, but it usually averaged around 11-11:30, every night that I was not at class. I work a half hour away from home so late nights. I also am up by about 5-5:30 every morning to go out and take care of horses, and all my other creatures, and then off to school or one of my other jobs. This last week also was the first week of school, so that means homework, like this blog, and studying also needs to find time in my schedule. A new horse also moved in this last week as a boarder and her previous owners did not take care of her or train her. So I have also been asked to assist in that process. So when is everything too much? When you can't keep your schedule straight? Is it when you don’t see members of your immediate household for 24-48 consecutive hours? When no one can find you, because they can't read your schedule?