Mine are 15 now (twins), so still some schooling to finish, but I am looking forward to getting my own life back again. I'm not saying things won't be a bit empty and strange when they first leave the nest, it is something though we all know would happen.
I say, rejoice in the fact you have done wonders, raising your children to become independent adults. After all, that is our job. As the others have said, look now at what you'd like to do with all this extra time you've on your hands. Let your children be as interested in hearing about your day as you will be of theirs when chatting.
Change, we all need time to adjust.