Suddenly hiding anthia

[toytech]

In my 120 I have a he/she lyertail Anthia and a Carberry he/she as well (both transitional),they are best buds and are out all day , have been in the tank for several months , voracious eaters fed multiple times a day , and get along with everyone in the tank(no big tangs or aggressive fish). Suddenly the carberry has been hiding in the rockwork , breathing has increased , will come out when food is put in the tank but wont eat . No new fish have been added recently and all other fish are acting normal . Ive read several posts of people having the same problem with different anthias but no one seems to have an answer why this happens and most seem to die , but I was hoping someone here has had a different experience . Not sure what to try at this point , QT ing him will probably finish him off , but I do have antibiotics I can use in the display, but I don't want to if I don't have to .