You may not end up being an empty nester, so don't stress over it yet. Plus, think positive . . . if you did a decent job of raising your child to be a responsible adult, that's a good thing. As a single parent of 3, I knew that I had to work myself out of a job so when my kids were ready to go into the world, they could, with confidence.
You will have a lot of freedom to do the things you want to do. Start planning on what you want to do with it. Get yourself ready. It's a whole new world out there and it can be yours.