I just got a new betta two days ago, and he constantly swims at the top of the tank?

I can't tell if what my fish has is Swim Bladder Disorder or not. Two days ago, I got my betta, and placed him in his aquarium. It is heated to the right temperature, and conditioned as well. And though he swims around, and is attentive enough if something causes him to be, he hardly EVER leaves the top of the tank. Still though, I've seen him also go to the bottom, and the middle, without much difficulty at all. He swims pretty parallel to the ground, without really any tipping, and he's able to hover in the center of the tank as if he's maintaining buoyancy. Not to mention his swimming isn't all that clumsy looking. On the same coin, though, he isn't eating, and his reaction to stimuli isn't all that great. (It's there, but not as alert as it seems it should be). He does flare when a reflection of himself is put alongside the bowl though. He also tends to float around more than actually swim and explore. Does this sound like SBD? Or is he maybe lethargic, or just likes the top of the silly tank?