We wrote four tunes that way. It was really great to realize that songwriting doesn't always have to be a painstakingly agonizing process. I've done it since then. I don't need to. If I don't write for a long time, I just accept it as a break and don't worry about it.
Inspiration comes in waves and that's fine.
I write so much that it's actually a relief when I don't want to write. I just keep going. Sometimes you have to write a whole lot of crap until you find something good. I don't believe in writer's block. You simply go through periods where you don't like everything you write.