You are completely normal!! When my DD moved out, I spent a whole week crying....but then I realized I could use her room as a full time sewing room :twisted:
Things to do that help: Rediscover your hubby; go on a quilting retreat with friends; re-do your sewing room; do those things that you haven't done that you've always wanted to but couldn't because you had a kid at home (weekend getaways with DH?), etc.
And don't forget to pat yourself on the back for doing a great job in raising him.... :D