asleep ~ акцентирует состояние
sleeping ~ акцентирует действие

ARE YOU ASLEEP is something we ask someone when we don’t know if they're sleeping because we’re both in a dark room, or they’re facing the other way. But we also ask this somewhat rhetorically when we need to talk to someone and they’re in bed with their eyes closed, but we mean to wake them up either way because it’s important to us. Also, just as often in this context, we ask ARE YOU AWAKE?

ARE YOU SLEEPING is a way of asking someone if they’ve been sleeping well lately because they look tired. We’re less likely to ask someone who’s visibly lying down with their eyes closed if they’re “sleeping."

Получается так:
ARE YOU ASLEEP? - Ты спишь? / Ты не спишь?
ARE YOU SLEEPING? - Ты что, не высыпаешься?

Ещё мой товарищ предложил:
Are you sleeping - что-то типа "Что это ты, прямо на ходу спишь?"

Благодарю)