They sleep in all kinds of crazy positions & places, though I'd check to make sure your temps. are good because he might be trying to cool off. Ambient room temp is just fine for them at night as long as it doesn't drop below the mid sixties F*.
Does he have a hide ??? If not I would get him one and then put something in there for him to burrow in like kleenex cut up paper towels soft cut up cloth -- I have a fleece blanket on the floor in his hide w/ some cut up soft paper shop towels for borrowing
Karrie