Does it sag as in like its melting(more likely you have wrinkles) or does it pull back as in like someone is pulling the back of your heads skin (thus making your face have no wrinkles)
How old are you? You shouldnt have saggy facial skin until much later in life when it really loses its elasticity. Wrinkles are more subtle and creep up from late 20s or so. Unless you sun worship a lot then they can come earlier.
If you're young with saggy skin from weight loss then surgery is an option. Facelifts work well with young skin because you still have good elasticity so it looks natural. It looks scary on older folk cause their skin has no natural stretch so it looks tight as a drum.