Pacing

I'm wondering and hoping that it is possible to stretch my teaching endurance.  How many hours can one teach in a row?  My schedule seems to get full so quickly and the coming year is looming as a busy one.  I remember reading something written by a psychotherapist that there is such a thing as compassion burnout.  And although I'm not  therapist I can understand.  It takes energy to be with somebody for an hour, and to not only attend to their needs, but to ask oneself what they are and how to bring them to the surface and how best to address them given the person's overall and current disposition.   Regardless of being tired, I usually enjoy the work I do enough that I can keep pulling out more energy if needed, but my body still has certain needs.  At the very least, it's making me more serious about my boundaries and also my expectations for those with whom I'm working.  And maybe I will be forced to find a more peaceful maintenance of myself that I may have longer phrases in general.