Self-publishing is one exhilarating ride. After you publish that book, you're on a 'high,' waiting to see if your book sells. It's thrilling to get your first sale, your first review (especially if it's a good review), and your first fan. You're at the peak, and unfortunately, the only place to go is down.
When you go down that hill, it's not as thrilling as the ride up, unlike on a roller coaster. It could be that you get your first bad review (they really sting, for all you troll haters out there), your sales momentum decreases, or you get some haters who are just plain mean. But be hopeful. When you're down, either the ride's over or you're on the way up again. And usually, you're on the way up.
So hang in there. There is always a light at the end of the tunnel and eventually, it'll all even out. Enjoy the ride and take more journeys by writing more books.
Have a great week!