There is a problem when the tail does not wag or the tail hangs down with little movement. It usually means that there is a trauma at the base of the tail.

It also happens often if the dog has been swimming in cold water. If this is the case, it will get better on its own.

Most vets will give a steroid injection or anti-inflammatories and it gets better with time.

You should see your vet as soon as you can and get treatment.

Keep in mind, also that anal gland problems can cause pain around the tail and the dog will hold the tail down because of it. He might also drag his bottom on the carpet or lick excessively.

So, expressing the anal glands could solve the problem for you! Your vet or groomer can help you with that. If the glands are infected, your vet can provide antibiotics. If this is a common problem for your dog, you can also have the vet teach you to express the glands yourself.

Let me know if you still have questions.