Unfortunately, or fortunately depending on the type of reception that Mat needs, Yennefer is not turned off by the outburst. If anything, there is a small part of her that is vaguely impressed that he's willing to yell back at her. But that feeling is not shown, and really the only thing Mat will see is the hardening of Yennefer's frown.

"Sit down." She says, firmly and sharply. It's an authoritative tone that Mat might have heard her use before, but only once or twice. There's an understood thread to it, too - that if he doesn't, she will make him. "If I'm to keep your mind intact, you are going to have to get it together and tell me exactly what you're seeing and hearing. Understood?"

It's only when he does sit (if he does) that she will reach over his shoulder to her desk, where there are various bottles and notes organized about. A continuation of her studies, it looks like, but she will look through a few of them before grabbing one and turning her attention back to him.

"You're not going to lose your mind. I won't let you."

Because she has to be able to keep someone else together, if not herself.