Yes, it sucks to think that your ideas are all used up when you are pressed for time to deliver a proposal. We designers like to think that we are artists, and artists constantly strive to create designs which are not only noteworthy of our clients, but more importantly, satisfy ourselves on a personal level. Yet when push comes to shove, the pressure causes one to burn out and create passionless work.
You are not alone - this happens to all artists and designers. I believe that it is due to the fact that we are people who are not satisfied with formulaic ways of doing things, but instead make every effort to explore new ways of driving home the message.
When the lull moment hits, most of us have to slog through the slump or just simply wait it out. But then again, if you can’t afford to wait it out, you might want to try reading this.