firstly, make sure he isn't floating lopsided. dunno if the upsidedown thing was a fluke. if he is floating lopsided, take him to a vet, they'll give him antibiotics for a possible respiratory infection.
in the meantime, make sure the little guy's water is at 85 degrees. no colder. they should be maintained at that temp. some will do fine, but for little guys esp one w/ a problem, 85 degress please, no less.
if he doesn't eat and you are really opposed to going to the vet, PM me, we'll MAKE him eat.
good luck, i hope it is not too late.