There's no such thing as sleep for a dog. There is only waiting. If you don't believe that, take a look at your dog's eyes the next time it's asleep. Its body language exhibits all the signs of a sleeping animal, but its eyes are open and it's decoding your body language for any indication of movement toward a more exciting place, like the food bowl or a room filled wall-to-wall with dog anuses ripe for a deep, contemplative sniffing.
Human owners have a radius of only about three feet they can move before a dog's internal adventure-sensors blare and it wakes up thinking it's Wendy, you're Peter, and it's time to revisit Neverland. Here's a slick graphic to help illustrate my point:
Take so much as a half step outside of the circle, and she shoots to attention, like I caught wind there's a raging kegger in the bedroom and the dog doesn't want to miss out on the Facebook selfie-fest that's about to go down: