It definitly sounds stressed and ich can take host to stressed fish. Look at the fish at night a good while after the lights have been out and also early in the morning before the lights come on. If you see white spots it has ich.

How low did the temperature get? Did any other water parameters change like salinity, alk, etc?

Is it eating? How are your ammonia, nitrite, and nitrate levels?

Just checking things that may have led to the stressing of the fish and what may need attention.