You can't click on them and sleep, like you can click on a chair and sit, but you can use the \sleep command to do the same thing.
In those early WoW days I took a lot of pictures of Keila and Karrah doing just that, sleeping.
Since I'm still the same goofy casual
player, I took a photo of Karrah sleeping in a bed in her garrison last night.
Technically, I guess this is her actual bed until another one comes along.
Keila the Forest Cat