Getting sick is always difficult when you're self-employed. If I were you I'd try and contact as many students as possible and then stick a note on the door saying all lessons cancelled due to sickness, apologies for the inconvenience.
Good policy, Bob. (How are you doing, bty?) They really should be leaving good contact information with you, anyway, and you can only do what you can do.
I only get sick during vacation. Like all decent teachers should .