Getting excited, coming up with features, buying domains, feeling doubt, questioning my sanity... I consider these all normal stages of product development.
Try thinking of them as road signs. They indicate you are getting closer to your destination. If any of these road signs are amiss, then start worrying (and check your pulse to make sure you're still alive).
It's the 'knowledge gap' trick. Create a bit of mystery - a mental itch if you want to call it that - and readers start drooling like Pavlov's dogs. The writing is good though, so I didn't mind.