I find that every year around the end of August/first of September I get really bummed out, no motivation, just a major slump. Then I get revived as soon as the weather starts to change and that crisp fall feeling starts up.

Now that I've figured it out, I give myself a break around this time of year and don't beat up on myself if I don't ride a lot. I try to do other activities and start to plan for fall riding and adding in some cross training as the daylight gets shorter.