I agree that if a chick sleeping on their side is otherwise fine, they are most likely to hot. If one ( that is otherwise fine, of course) goes right under the lamp in the hottest spot they can find and sleep like that, they are just being silly and will grow up fine. If their legs flop out limply behind them, that's not a good sign.I was speaking only about the issues I have had with seramas and failure to thrive. I have noticed with the ones that fail to thrive and die, they will start laying on their sides and back when they sleep, I will turn them back over but they always sleep only on their sides and backs. If you have other breeds besides seramas that scretch out and sleep on their sides with their wings up they are too hot and trying to cool off. I do not have this failure to thrive with any other breeds but seramas.
I unfortunately have no experience with tiny, pure serama chicks. I turned up to get my serama eggs- the hens at least looked like OEGB x Serama to me. But, they were free! With chickens, the more the better, right?