It happens every single time. It's the same exact bed, in the same exact spot. And yet, every time one of our dogs goes to lay down on it, they spin around several times and finally lay down and let out a huffing sound. Sometimes they dig in with their paws, and other times they root around with their nose.
Have you ever wondered why your dog does that? Is it anxiety? Some canine form of OCD? Actually it appears to be more evolutionary than that. There seems to be two different trains of thought about why this happens.
One theory is that the dog is making himself a den. Our dog's ancestors would have to create their own shelters and beds. If this was in tall grass, that would involve spinning in circles to flatten the grass and make a bed. In other landscapes, a dog might have had to dig down to cooler soil to escape the heat. Any thing that needed to be done to make a comfortable bed for the night. Similar to a dog that will push all his blankets into a corner of his crate, or using her nose to push pillows around.
Another theory is that it is a sort of protection instinct. Dogs may have spun around while scanning their environment looking for predators. Once sufficiently satisfied that they are safe, they will settle in for the night. This may also explain why some dogs love the relative solitude of a crate. They feel safe and secure in their "den" and it makes it easier for some dogs to settle in a crate.