When you see your sweet pup sleeping on his back with all four legs in the air you may think he looks silly, but your dog is about as content and comfortable as he can be. Just like people, dogs have different stages of sleep and different sleep positions.
Back sleeping is the most comfortable position for a dog because it allows his muscles to completely relax. When a dog sleeps on his stomach, on his side or curled up, his muscles are still tensed. These positions all allow a dog to wake up and stand up quickly. When a dog is sleeping on his back his muscles are un-tensed, he is at his most relaxed state and he is in deep sleep mode.
Dogs also sleep on their backs to cool off. Whether a dog is hot because of the weather or because he has been exercising, exposing his stomach is a speedy solution for cooling. A dog’s stomach has the least fur on his body, so exposing it is kind of like switching from a heavy coat to a lighter one. This position is especially helpful for dogs because, unlike people, they have sweat glands only on their paws.
Back sleeping is a position domestic dogs choose not only for comfort and cooling, but because they feel safe in their environments. It only occurs indoors. Wild dogs and wolves do not sleep on their backs because the position leaves them vulnerable. They generally sleep curled up to protect their bodies and so they can get up quickly when they feel threatened. Domestic dogs who are kept outside take after their wild counterparts when it comes to sleeping; they don't sleep on their backs either.
Some dogs lie against their owner or another dog while sleeping on their backs (they may also do this while sleeping on their sides). This closeness indicates that the dog is fully trusting and wants to demonstrate his affection for his owner or canine relative. Sleeping in this close position is also a way that dogs bond with and protect their loved ones.
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