What you're describing is EXACTLY how I felt when I started taking Buspar. But now I wonder: Aren't those feelings a sign that we are way too anxious? Would someone who didn't share these anxiety "issues" stay awake at night over-analyzing, attempting to predict, constantly worrying about a medication that has been proven to be effective and that we're taking under a dr's watch? I don't think so.
I think from you've written here and your consultation with your GP that this is the right time to start. If Prozac ends up not working for you, I'm sure she would help you find a different AD.
How are your girlfriend and family supporting you during this time?