Please help quick!

[Brickywan-kenobi]

Okay, so I have a synodontis petricola who has been acting strange, I think he might be sick. I just did a 50% water change and when I reconnected everything I saw him lying on the ground not moving around besides flicking his fins and gills. He's breathing a little fast, but looks healthy. My ammonia and nitrites are at 0, but my nitrates were a little high (around 80ppm), which was why I changed the water in the first place. What should I do? I don't want my fish to die if I can do anything to help him.