Yuya lets out a long, low wheeze. His shoulder slowly relax and, yes, Tamaki did scare him--but he's not going to give him the verbal confirmation of it. His reaction is probably enough.

"Were you hiding there this whole time?!" 'There' being... behind the couch? Tamaki is seven feet and there's no logical place he could have been hiding to begin with, but it also isn't logical that he can teleport. Or sneak in without squeaking the door.