Ever heard of spraining a tail?

No I am not kidding....My housemates poor dog actually sprained her tail...This would be funny but she is in so much pain!!! Poor thing....She's a golden retriever who loves everyone...I can see why she sprained it-I'm just amazed it took this long for it to happen...She's 8yrs old you know. She cries and looks at you like...What happened? FIX IT! Please????