IME those fish just act that way. My Royal Gramma only hung out in one are of my tank for months and still only stays on the left 1/4 of the tank when he is outside of his hiding spot. Sounds to me like you stressed out a fish that was healthy to begin with.
How long was it in your main tank before you put it into the QT it is in now?
Was it eating in the main tank?
You mentioned you are treating it for ich, did you see white spots on the fish?
180-gallon acrylic mainly SPS, SWC 1A Cone Skimmer, APEX Neptune Controller, 3x MP40w Vortechs, Tunze 6045, Radiums 250w in Lumenarc Minis, Galaxy Ballast, BRS Dosers