Istredd's never seen anyone let themselves get sick in here, which means that this is very deep into Wilhelm's psyche. He is struggling with something so severe mentally that he can convince his body to vomit. That's some deep issues. He is concerned for certain, waving a hand and the vomit simply disappears, because it isn't real here. None of this is real.

"You don't have to be sorry. It's fine, Wilhelm. I'm glad you're willing to keep trying. That's important." Rather than give up, which would help no one. Istredd can't help him in this situation until they work more together and he puts himself in a position where he can provide more guidance.

His gaze is sympathetic. "Go get some rest."