Most of the time, dogs choose to snooze with their bellies facing down. This is done for two reasons: comfort and security. For centuries, dogs in the wild have curled up into a little ball while sleeping to keep warm on a cold night and to protect their vital organs from potential predators. Most domesticated canines tend to follow this rule and catch their z’s resting comfortably on their tummies. However, there’s always an exception to the rule.
A small percentage of dogs, around 5 to 10 percent, sleep with their bellies exposed to the air. Many factors can contribute to this behavior. Dogs that have a relaxed personality may be more likely to sleep on their backs. These are the dogs that are most temperamentally different from their wild ancestors. In other cases, dogs that are well-socialized, confident, and feel extremely safe in their own home might assume the belly-up sleeping position. Dogs with a shy personality aren’t likely to be comfortable with feeling so exposed.
Lastly, a dog’s sleeping position is sometimes simply a matter of preference. Some dogs just find it more comfy to roll over on their back during nap time.