Stress
When half the school (including teachers) is quarantined with the chicken pox, and it's up to you to find subs for almost every class ASAP, you might need to do a little yoga or meditate—after you handle the problem of course.
This is just as stressful a job as the school principal's. Well, almost as stressful. If things go really wrong, at least it's not your head on the chopping block...first. But you'll be right up there second. Make sure everything runs smoothly and nobody will get hurt.