Cas internally flinches a bit (the only outer reaction is a blink) at Dean's terse response. Even if Castiel were in the habit of reading thoughts, there would be no need in this situation: it's obvious that Dean is not fine.

He half-smiles at Dean's immediate apology, and decides not to point out that he isn't a doctor, as he suspects Dean doesn't mean it literally.

"I feel... strange. Unsettled."

More to the point, he feels. Which is nothing new, but the direction of these feelings is. He has never felt a particular urge to have someone to hate, for instance.

That's different from smiting, shush.