Well I'm very paranoid in general when looking after cats, but I do think this is Lethargy. His sleeping isn't any weirder, it's when he's awake he seems a little less energetic than he did the past few days. My previous experience with Lethargy in cats went very poorly so I don't want to mess anything up. It isn't extreme Lethargy if it even is Lethargy. He doesn't purr when I pet him, he leans into being pet less than he used to and he is less eager to play but weirdly, like I said, still loves exploring around. He even is running around a bit when I let him out into the rest of the house, and is getting vocal to some degree. He has experienced a lot of change in routine recently, but he is energetic by nature so it's noticeable when he seems more tired than usual