I have to laugh at what annagybe said, because I would also cry (great big heaving sobs) if my pants from 2005 fit too. Back in 2005, I was about 90 pounds heavier than I am now. Yikes!
That said though, I can totally relate to the joy in finding something old that fits that you didn't think you'd fit into again - so yay!!!
Are they nice pants that you want to wear again?