There are times when every teacher needs some inspiration. There will always be days where everything goes wrong and the idea that anyone actually learns anything in your class seems remote. We all need inspiration now and then and I believe you should not ignore those needs. We are human.
One recommendation—the next time you are down and out about teaching, go to the video store and check out a movie from 1988 titled Stand and Deliver. You cannot possibly watch that movie without getting excited about the joys of teaching. It is the true story of a Los Angeles high school math teacher in a very poor area who drives his students to succeed on the AP test for calculus. He pushes them so hard that his students are accused of cheating because they do so well on the exam. They all forced to take the test a second time and they come back and pass it again.
No matter what the problems they encountered, the teacher did not let his students give up. He willed them to succeed.
It is just a wonderful story of how one teacher is able to make such a difference in the lives of so many young people by pushing them to be great. Watch it one night and you will be a better teacher the next day.