I have a 14 year old 80lb mutt that has recently started staying out all night after a lifetime otherwise?

The yard is secure except for an occaissional skunk, but she is not a" chaser" . I live in San Diego so the weather is usually mild, but my concern is that she seems so stiff when she gets up. I have two mutts about the same age, but staying outside at night is new and unusual behavior for her. ... should i be worried ?