This morning I noticed that Stripe, Kameko, and Odyssea were all doing headstands lol, Kameko is the worst, he's on a 90 degree angle, Stripe is better now but he was doing it too at first. Kameko is swimming around again bit still on that same angle. Im really worried about them what should I do? I dont want anything to happen to them especially since Stripe is special cause he was my very first fish and survived everything, and Kameko's fins have finally grown back (except a small tear in in dorsal and anal fin), he's so pretty now, I have a video of tem doing this I'll post later. I also saw a small black mark on Stripe and tested for ammonia but its still at zero, anyone have any ideas whats wrong with them? Btw, its a 5 gallon tank with a Elite Hush 5 filter.

they're all back to normal now

When I used to have tiger barbs they stood on their head while they were sleeping. I had a school of six, and late one night I walked into the lounge room and noticed that all my tigerbarbs were in a group, all on their heads. It looked bizarre. When I came up for a closer inspection I must have woke them because they went back to swimming normally

it wasnt at night though but at least they're better now