If your dog isn't chasing their tail, then why are they spinning in circles? I've seen dogs spin in circles before laying down or even before using the restroom. Dogs spin for various reasons:
Spinning before going to the restroom ritual -
Turns out dogs who spin in circles before using the restroom have retained this from their ancestors. Circling before squatting was how their ancestors would investigate and secure their surroundings before vulnerably squatting to go to the restroom. Preventing any...BAM...surprise attacks. Some say this also allows dogs to quickly wake their digestive system.
Looks like it's time for a nap? -
This may be the more common ritual that dog owners see from their fur-baby(ies). Believe it or not they spin in circles on their bed to release their scent glands. This serves as a signal that the bed belongs to them, and them alone. In addition, to releasing scent glands by circling your dog may also release scent glands by completing the ritual with digging. The digging may also serve as a way to warm up and soften the bed before they lay down.
The "I'm so happy to see you spin" -
I'm not sure about your fur-baby(ies) but when I get home my girl gives me the wiggle-butt greeting while holding her toy duckie and giving me the ruff-hello. There are even times she'll start spinning in circles when she sees me. Clearly I'm dog mom of the year!
Note: some dogs may excessively spin and begin to ignore their food or need to sleep. In these cases I recommend reaching out to your veterinarian.