Why does my dog curl up to sleep? Dogs in the wild curl up to keep themselves warm, and to protect their soft undersides from predators. For extra protection and warmth, they often dig out a nest to sleep in and the instinct to curl up remains in our domesticated dogs. Many dogs like having a small bed or something soft where they can “dig” out their nest. If your dog stretches out to sleep, they feel safe and secure. And, probably warm.