Dog standing on rear tip toe with tail tucked under

After coming home from work I called my 8 year old pit bull mix Rocky to go out. He did not come as usual. I found him standing in my bedroom on his rear tip toes and his tail tucked between his legs. He tried to walk on them but was having difficulty. I felt is legs, hind qaurter area, abdomen and tail with no obvious injures and he did not appear in any discomfort or pain. I helped him to his bed to rest. This condition continues today. I have seen him stand like this before after getting up from a lying position but he usually recovers after a moment or so. I am very worried now. Can anyone help? I do have pictures I can send if needed. Please email me at [email protected] with comments.

A trip to the vet is in order, it sounds like it might be something related to his spine. Whether it is nerve damage or arthritis, it is worth getting it checked out, the tail being tucked down clear say either spine (as the tail is a continuation of the spine) or he was in pain, so that's not something you want to keep happening, poor guy!