It's very helpful to tell if he's ok if you have a gram scale to check him out with. Chances are, he's just snoozing because it's winter and there's nothing to worry about. If that's the case, then he wouldn't lose any significant weight - if he dropped a lot, then something's wrong. Keep a close eye on him, though, and if you really feel like something's wrong (or he has other symptoms or strange behaviors), and you don't have access to a scale, get him to a vet for a check.
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Torey
Eugene, Oregon, USA
1.1 Uromastyx Geyri (Joe and Arthur)
2.0.1 Uromastyx Dispar Maliensis (Tank, Turtle, and Spike)
1.2 Anolis Carolinensis (Bowser, Leeloo, and Sprocket)
1.1 African Dwarf Frogs (Bruce and Sheila)
1.0 Betta Splendens (Mr. Miagi)
1.1 Felis Domesticus (Roscolux and Jenny)
And several miscellaneous community fish
