Heheh. I have a Gillens Tree frog (close relative) that I've called Jeff. He sleeps through everything and even at night he is usually asleep. He's not sick, just lazy ! Even when he's up and about he goes and takes naps. I've seen him not move for two days straight. He also has a weird habit of placing his head under any frog above him's backside.... I think he finds it comfiest O.o. Mine have never moved in the day.

You'd think he'd have a weight issue but actually he's pretty much ideal. The hyperactive one is a bit skinny due to him being more hyper than a 5 year old drinking red cordial with ADHD. He likes to sleep on top of other frog's heads....

Polar opposites and best friends they are XD.

Frogs have quite a bit of personality and I think sleep's related to how they're feeling. As long as they are sleeping and healthy....

He may have moved about to move to a warmer/cooler spot. In that way if there's natural temperature variation it could be "seasonal". Or to a drier/more humid spot.