It happens. Getting excited about your own story is important because it is what essentially motivates you half of the time if not the readers. When it happened to me, it felt like hell, I committed more fumbles, I felt like I was clocking in for a job I didn't want. If you are writing to earn money, I suggest having a secondary or tertiary project where you have the least commitment and feel comfortable abandoning when you feel like you have that spark of excitement again for your main project. I don't recommend taking a break in the middle of the story, because it could suffer the quality of the story or your readership in general. Do it after the end of an arc or the end of a book. Of course, if you really can't take it anymore and see your writing is suffering that badly, inform the readers and tell them you'd be back. I don't suggest leaving them with a bad chapter though, where they literall have to tell you how it sucked and doesn't make sense. This happened to me, and its bad.
Edit: Even if you are not writing and profiting, I still suggest taking a secondary or tertiary project, because that usually takes the edge off. That was the case for me. Heck, I wrote a worldhopping novel when I was on my burnt out phase and got tiered of my main project. I eventually got back in the groove after finishing the Book 1.