Take a break! I hit a dead spot at the end of the race season also. I think the body needs some down-time in the fall as a natural response to shorter days, colder weather, I think our bodies naturally want to hybernate. Let it. Take a little down-time, relax, do something else. I hunted a lot this fall and it helped put some lean meat in the freezer. Then pick a drop-dead date to start back into your training plan fresh and wanting to get back at it.