If you are interested in one of facts why endurance training makes you so tired then read this article from the New York Times about »Sleep After Hard Workouts? You Must Be Dreaming«
Endurance training stimulates the immune system and induces among others the release of the cytokines Interleukin-6 and tumor necrosis factor alpha. These 2 cytokines are not only initiators of inflammatory processes in the muscle but have central nervous effects as well. They are in part the culprits for excessive sleepiness.
Take a break from training, if your are tired. Overreaching may result in overtraining, burn-out or chronic fatigue syndrome. Intact immunity is essential for peak performance. This applies for athletes as well as for people stressed because of various reasons.
Biestmilch is a wonderful substance to mitigate stress phenomena and relax a tensed a immune system.
