loach ill or old?

[mousey]

N. Corica is having a hard time breathing. Has been tearing around the tank in the day time with the occasional foray to the top. Crashing into the sides of the tank , falling onto his back.
have had him for about 3 years now.
He is the survivor from my original 4.
tried him with a few crushed snails but he seems dazed. Currently in a breeding box for observation. Not making any attempt to jump out. he is usually fairly reclusive and plays in the dark, so this daytime swimming around seems to be an ominous sign. I have no idea if it is just an illness or if he is dying of old age or if something is stuck in his throat..
I have not added anything new to the tank for the past year. Water specs are 0,0, 15-20. tank maintenance done q 2 weeks, 30% as I have followed the past 5 years.
Ideas please? he is the only fish in that tank that is having problems.