Well this is a weird one. New to me anyway.
A couple of weeks ago I noticed Gassie (the drop-dead gorgeous English Setter we adopted) was holding his tail in a very odd way. As it is usually carried banner-like behind him while he races along, this was immediately obvious. He was holding it close to his body, following the contours of his hind legs and seemed to be in some discomfort and not able to sit down.
As the vet's was closed, I leapt online and a bit of research led me to a strange condition afflicting Setters and other cani di caccia. Known as 'cold tail' or 'lumber tail' it strikes without warning and can be brought on by a change of weather, over exertion or getting chilled. (Probably all three in Gassie's case!) The tail is held close to the body, and is kind of paralysed. It sometimes appears to be extended for a couple of inches and then hands down limply. It is not broken or damaged and usually heals on its own. The treatment is rest and aspirin if absolutely necessary.
Careful examination of his tail proved there was nothing broken, and after 24 hours Gassie seemed better, not in pain, but was still holding his tail down. I didn't give him aspirin as I don't like to medicate unless absouletly necessary.
As the days have passed he has regained the use of the tail and now, two weeks to the day, he is wagging it and can sit down again. He has become even more boisterous (if that is possible) and seems none the worse for being struck down with this mysterious ailment.
So just to reassure you if your dog's tail is afflicted with this odd symptom, once you have excluded breakages and wounds, it is probably 'cold tail' and is something best left to get better on its own.