When you dread a ride it is time to rest, as said. I disagree with the post that said you just didn't train hard enough. Part of the cycle of strength building for muscles is rest to allow the muscle tissue to begin rebuilding and to flush out the waste and toxins built up from the exertion. If you have dome really hard workouts to build up you need the time to rebuild and rest.

Your replies said what I think you already know about the need to back down from time to time. Just take a day off or at least spin leisurely for your miles.