Why did this happen?

[Coralix9]

My Betta did this when I used a new water conditioner. Maybe check if you changed products recently.

[FinleyRise]

Bettas are just weird like that sometimes. Mine once zoomed around for no reason and then went back to normal. Could just be a phase.

[yoyer]

I'd test for copper if you've used any meds lately. Even small amounts can mess with them.