He just likes to sleep upside down on the surface of his tank.
Actually, it's the dreaded swim bladder disease. It happens because they've been bred to be "fancy": i.e. egg-shaped, which screws with their air bladders.
It's hard to get a good shot of him when he's upright as he has to swim constantly or he'll flip over and float to the top.
Is he suffering? Happy? Should we put him out of his misery? Maybe he's okay with his rotated view of the world. Several other fish we've had have lived for as long as a year like this. It's very distressing to look at, but when he's right-side up, he seems happy, cruising around looking for food as usual.
Don't buy fancy goldfish - it only leads to heartache.
*With a tip 'o' the blogging hat to Cathi D. (Yes, I have a thing for her. And her chickens).