In this case, you can use the universal letter from the English alphabet zzZ. We know its meaning from various cartoons. It means snoring and sniffing. It is not difficult to show a pillow so that it is clear that the person is sleeping [ ]. There are variations with the mouth slightly open and always closed eyes (two horizontal lines).
|(￣o￣) zzZZzzZZ||(( _ _ ))..zzzZZ|
|(＿ ＿*) Z z z||(x . x) ~~zzZ|