I can't sleep in earrings of any kind, especially studs. The posts stick into my neck. I don't know if others have the same problem- I have very "flat to my head" ears and that might be why studs aren't comfy. DH and DD, who have ears that stick out and away from their heads more, make fun of me for my freakishly small ears. I can't wear earbuds- they are too big to fit in my ears.
DD has pierced ears, and wears her studs 24/7, with no complaints.