You know how sometimes you have nightmares where you try to call out but no sound comes out? (Well, maybe you personally don't, but it's a very common dream.) That's what the author is referring to; the protagonist doesn't necessarily dream that he has laryngitis, but it's used as a kind of metaphor. It's probably the most elegant way of expressing it.
"Eschew" means "avoid"; here, it's used to mean "deliberately choose not to use". "Raiment" is an old-fashioned word for "clothes".