Dogs like humans differ in so many ways. Even dogs of the same breed would manifest different personalities. While it is basically common for dogs to form a strong attachment with its master, some are known to be very dependent to the human family than others. Dogs would have different habits too. The size of the dog does not signify its actual personality. A large breed like a Great Dane can be a little miss prim and proper while a small Yorkshire Terrier can be like a thug that would harass not only rats but intruders and strangers that would prove to be a threat to its master. Dogs differ even in the way they sleep. Some would stretch out and occupy the whole doggie bed, others would lie on its back and others would sleep curled up. Of course the sleeping position of the dog would have different meanings.
Obviously a dog curls up when it sleeps to conserve warmth in the same way that humans curl up under the blanket when it is cold. Fortunately, we humans have blanket to keep us warm. The tail especially if it is bushy serves as the dogs blanket. When a dog curls into a ball it can easily cover the nose with the tail and the paws will be covered with the body. This sleeping position is most common in dogs that sleep outside the house. In bygone days when dogs live in the wild, the dogs would bed on the snow and on the ground. Dogs would paw and trample the vegetation and the snow to make the bed a little more comfortable. As the sleeping area would be open to the elements, the dog, out of necessity would need to curl into a ball for warmth. Dogs in a pack sleeps together usually in a den. The den would be sheltered but in most cases it would be a cramped area. Dogs therefore would need to sleep curled into a ball to make room and accommodate other members of the pack. For thousands of years the dog has become the constant companion of humans. After domestication dogs were given all the comforts imaginable. Our best friends were not only given regular supply of food but also given a warm and comfortable nook for their sleeping quarters. In most cases the dog will have spacious, soft and warm mammoth beds. Some are even allowed to share the bed of the master. Alas, the dog would still curl into a ball and occupy a small portion of the bed. After years of domestication, the inherent trait of sleeping curled still kicks in.
Another reason why dogs sleep curled up is for security. When the dog curls into a ball, the stomach, the throat and all the vital organs are protected as the skeleton would be on the outer side. This position protects the dog from predators attacks. Dogs are very particular where they sleep. Owners are often disconcerted as in spite of a comfortable bed the dog would insist in curling into a ball under the stairs, under tables and even in closets.
Curled into a tight ball is not the most comfortable sleeping position of a dog. In this position the dog will not have a restful deep sleep. To be able to maintain the curled up position; the muscles would be all tensed up. When the muscles are not relaxed the dog would not be able to enter the rapid eye movement (REM) stage of sleep. Dogs sleeping in this position would have a poor quality of rest. Relaxed sleep promotes good blood circulation that is vital for cell regeneration.
A bed designed to give the dog maximum comfort and at the same time give the dog a sense of security is highly recommended. Cup beds or donut beds with bolster wall on all sides are the best choices for a pet that loves to curl into a ball.