Clownfish swimming at surface slightly tilted?

[k1ngofthrones]

I’ve had my clownfish for three months with no problems. This morning, I noticed he’s been staying on the surfacing, swimming slightly tilted to the side as if one of his side fins weren’t working. He doesn’t have any spots on him or anything, what’s going on?

 

[Tahoe61]

Was the fish asleep, were the lights off or did the lights just come on?