Cory swimming weirdly

[Ktrk]

Hi,
Wonder if anyone has any idea what is going on with one of my panda Cory's..
We've come home from a kids party and he's in the corner looking like he's swimming his butt off with his tail going, but he's not actually getting anywhere/moving. Like if a fish was treading water!

He was fine before we left at lunch and the other Cory's are acting normally, as are the tetra so it's not a filter flow issue.

I've checked my water and nothing abnormal.
I'm stumped!

Thanks for any input

 

[Aiken Drum]

Could you put a video on youtube or similar and post a link?

Might also be worth going through the "unhealthy fish" sticky and answering the questions as thoroughly as possible.

https://www.aquariumadvice.com/forums/f17/before-posting-about-unhealthy-fish-read-this-32451.html