Yep, got that too - a few years ago now, for absolutely no reason, and it was really painful, especially during yoga, and lasted for ages - about a year, I think.
I was careful not to sit on hard floors (well, it was too painful to!), bolstered myself up with thick cushions when I could but generally felt miserable the whole time.
Like all the other weird meno symptoms, it started from nothing and just as suddenly stopped.