otherwise active cory is spinning

I have a lone 3-stripe cory in my 10 gallon tank. He has no other tankmates right now. The other fish were taken out a few weeks ago by an illness I never could diagnose. He used to have brothers but they are gone.

Anyways, he is very active and happy like usual. About 10% of the times I watch him, he kind of spins. It might not be a full roll, maybe a half roll sometimes. He doesn't rub on anything. The roll just happens while he's swimming around. This has been present for the past few days. I google searched and came up with a possible stroke?

Ammonia: 0
Nitrite: 0
Nitrate: 15
sand substrate
78F

Any ideas what this could be? (The other fish did not show this symptom at all, and he shows none of theirs, so I believe this is a separate incident.)

It's like a tic....

he's always been a strange one though.... wiggling up and down the walls and back and forth.... he used to get the others to do it too, but they were never as enthusiastic. He's always been very vigorous in his swimming and browsing... and now he just twitches into rolls and half rolls..... (I will be so sad if this develops any further!)