Aquariums: Possibly neurological issues with my dojo loach

I have a 75 gallon tank with 5 dojo loaches and 5 corydoras. the tank temp sits in the high 60s and on Sunday I cleaned my tank. I did everything I normally do, a 50% water change, scrape and vacuum the algae off the glass and this time I cleaned my filter (seachem tidal 110 HOB). I cleaned it in tank water and everything was mostly normal.

one of my loaches started swimming uncontrollably and super fast all over the tank. sometimes he does this if something spooks him so I didn't think much of it. afterwards he was just laying on the sand on his side breathing heavy.

the next day (Monday) I saw him leaning against the back under a bunch of plants in the dark. I figured he hit his head and I turned the lights off to help any head injury and stress. then I saw him swimming in a circle the way he was in the video but not for as long. I didn't know what to do but at that point he was still eating so I just kept my eye on him.

on Tuesday it was the same thing. lights off, same loach in the same spot, barely breathing. I fed them and that time he didn't eat and didn't show any interest in eating at all.

today (Wednesday) It was the same thing but the circles came back. the video I attached was recorded about 10 minutes ago at the time of writing. I am at an absolute loss and don't know what to do. if you're in the hobby you know how hard it is to say goodbye to one of your beloved pets especially if you don't know what could have caused the death in the first place. he's still alive right now but I don't know how much longer he will be. any advice at all or even any interaction with the post means so much to me. I'm also new to reddit and don't know exactly how it works.

also another note is that all my other loaches are fine and acting normal. all my parameters were good and like they normally are. any advice would help me a ton, thank you so much.