Rehearsals while sick can be a blessing. No matter what role you are in the ensemble.
As a singer, you can take notes and listen, often learning more than you usually do in rehearsal. Even if you can’t sing a note, being at a rehearsal can be so beneficial.
As the conductor, I often find that a two-hour rehearsal while sick can be a big part of getting myself over the illness. Now, there is a certain level of sickness above which I will not drag myself to rehearsal – I’ll get a sub or have my rehearsal run by section leaders. But below that level, I find that rehearsing through my sniffle, headache, post-nasal drip, etc. can be invigorating. I often have particularly effective rehearsals when I have to fight through an illness-induced headwind.
I don’t wish for illness. I’m happy to be well on rehearsal nights. But I don’t discount the progress, the fun, or the personal improvement that will come during a rehearsal while sick.