dragonet HELP PLEASE

[golden69_ca]

every thing was fine in the tank today nothing out of the norm . went out to the store when i cam back my lights were of ,normal so i set up my red light to check on the tank when i noticed my green dragonet sitting on a rock not moving or breathing with no color at all .in a mad panick i got a container and put him in it when i touched him he started to breath heavely and a slight color came back . i put hime in my 20gal isolation tank does this fish loses it color when it sleeps ? any help would be apreceated . he has been eating fine lots of natural food for him .