I inherited a fish who was like that, Fishy-San.
He lived for quite a while being all lazy like that, sitting on the bottom or in some plant, coming up for air and food.
If you have some plant, or something he can rest on closer to the surface so he doesn't have as far to swim, it might make him more comfortable.
I had a weak filter, and he'd swim up to the intake and stick himself to it, and pop off from that for air whenever he felt like it, then go back to reattach. I turned the filter off when he took up doing that, and he'd just hook a fin through and hold on instead. So something to sit on might be good for him.