Hi,
I was where you are 1 month ago and am now 2 weeks post-op. What you describe is the same for all of us who get close to the big day. The demons on the shoulder will always give you doubts and fears. Human nature means you will spend some time listening to these negatives but as you describe you KNOW the positives far outweigh these. Focus on the postives during you pre-op diet and very soon, like me and many others on the forum, you'll be writing supportive posts to pre-oppers!
Good luck and report back.
Craig