so far I agree with what people have said! If you are just remaining tired, become more irritable than usual, lower than normal sex drive, crave sugar!, are constantly sore....all are signs to ease up. If you ride regularly and can't live without riding for a day then your "rest" days must become weight free and easy on the bike. I've always been a big weight lifter and over the last 4 years started getting into endurance/ultra sports. The 2 don't mix well but it is feasible. just be reasonable. If your tired, and riding is your passion, but hopping on the bike sounds dreadful, then tone your overtraining. What I've learned is that just because your working different muscle groups doesn't mean you can't burn out.
Hope this makes sense I typed it on my phone :/