Chin less active than usual?

Henry has seemed sort of quieter for a while now, I thought at first that maybe he was getting used to his new cage and the presence of the girls (they're not too close but across the room from him), but now I'm not sure. I've heard him whimper quite loud I think in his sleep a few times, though I know they just do that sometimes. I was concerned he might be eating less pellets, but it does seem he's still eating, after monitoring more closely, and hopefully his teeth are Ok since he's still able to strip the bark off sticks. He's still lively enough when he comes out of the cage for playtime, it's just in the cage he seems less active, and not as interested in and responsive to things, or as playful and destructive (he used to destroy everything, but has ignored or quickly gave up on several toys). He's still chewed up the small vine ball I gave him last night, so it's not as though he's doing nothing, it's just he spends a lot more time just sitting there than he usually would've (I wondered if his breathing was a little faster but not sure if that's just because I'm looking to find something more obviously wrong, also although the room isn't too hot one ear seemed to be down and red quite a few times). I don't know, he just seems less active than usual.

I can take him to the vet of course but they don't see that many chins, and I'm not really sure what they should be looking for if I take him, so wanted to ask advice first.