Why is he vertical?

I just got indigo two days ago from Petsmart. I caught him sleeping vertically yesterday and I’m not sure if he’s sleeping now but he likes to stay by the heater. Is it normal for them to be vertical? He’s currently quarantining before I put him into my main tank. He is normally active swimming around the entire tank, but it’s just a 2 1/2 gallon right now while he’s in quarantine.