Unless you're up all night (which I doubt) it's very possible he's sneaking around when you're not looking. He's still new, so his daytime activity is pretty normal- it's because he's somewhat stressed* from being in a new place, but don't worry, *apparently he's adjusting pretty well, since he's eating. And he might be sleeping more at night just because his daytime activity is tiring him out. In time he should calm down more.