Do some bettas just like to sleep on their tail?

[TRISHIESfishie]

I know most if not all fish sleep horizontal and when they begin sleeping vertical there is a problem. Well yesterday King came out of treatment (after 10 days) and after swimming around and checking our his home it was time to sleep (for me and him) he starting trying to go behind the filter but I blocked it and then he started resting "on his tail". He is not acting sick yet and it swimming normal and eating and tonight he is sleeping horizontal. It made me wonder do some bettas sleep on their tails by choice? I hate freaking out everytime I see him resting like that