Am I That Invisible?

You can tell a lot about your friends based on how they react to your not being at work or in this case not being at work for three days in a row! After twenty plus years of being in the teaching profession, none of my colleagues' reactions can actually cause me to feel surprised anymore (at least, that's what I thought!). In any case, it is actually expected of them! I have been missing from duty for three days in a row; the first day I took two bus loads of students out on an excursion and the second and third day I was out on medical leave.
It was rather heart-warming to hear a few friends asking where I was and if I was feeling better; a few said they wondered why they had not seen me for three days. But it was quite disheartening (I should be immuned to this already, based on the number of years I've been in this profession!) when a few did not even realise that I was not in school! Is this a sign that I am dispensable? Or is this a sign that my presence all these years have not left any impact at all? To friends who cared, thank you. And to those who couldn't care less, I guess the feeling is mutual.