One of the most irritating things about being an group exercise instructor is the fact that, if you ever build a following (which you will want to in the beginning), you eventually become a prisoner and slave of it. It is nice to have a bunch of people who continually attend your class with such adoration and fervor. Unfortunately, this adulation eventually becomes obsession. Which leads to you being treated as an object eventually leading to your hatred for the followers you desired in the first place.
One of my biggest pet peeves is when I would tell my class that I will not be teaching next week only to be greeted with heavy sighs and queries as to what could possibly be the reason for me not being there. In the beginning you become apologetic for not being able to be there for them. I am sure part of it is the ego boost we all get from a group of persons wanting to be in our realm. It can be intoxicating to have some relative stranger profess how your absence will create a rift in their status quo.
As you continue to teach, you become resentful for having to explain why you are taking that specific day off from teaching. The burden of trying to find an excuse for or even explain your absence becomes overwhelming forcing you to think evil thoughts of your groupies. Eventually, you grow to hate your following because of their lack of consideration for you as a human being. You wonder why these people cannot see that you too have to take some time off and that you do not owe them anything except the responsibility of finding someone to teach your class.
As I near the end of my teaching career, I realize that I no longer explain to my regulars why I am going to be absent from teaching that class next week. The "regulars" that do understand me accept my announcement and go on their way. The regulars who cannot see me beyond being a group exericse instructor tend to ask for an explanation to why I will not be teaching next week. My answer has now become, "Because I need time away from here." It doesn't really tell them what I am doing (which is really none of their business), it shows them that they are not in charge of my actions, and it also kinda alludes to the fact that their neediness may be a factor in my absence.
So, if you ever get irritated that your favorite instructor is not teaching for a couple of days, just remember that 1) it is really none of your business as to why they aren't going to teach, 2) they have the right to not-teach the class, 3) and just like you, your favorite instructor is a human being who needs time away from their daily routine. Later.