Cold Sweats After Running, Excessively Tired. On Huge Diet. What Does It Look Like?

Hi, im a 28 Year old male. I have competed in Ironman events, 12hr & 24 hr races so im relatively fit and healthy. The reason i write is now and then when training, it may only be while 2 miles into a run i suddenly get a cold sweat and have to stop. by the time ive walked home i usually feel ok again. My other main symptom is i become excessively tired usually between 4 - 7 pm. if i sleep for just 30mins im fine again but the urge to sleep is overpowering and i almost have no control. My tiredness doesnt seem to be afected by diet or excercise, it can happen to me after 3 days of no excercise and even if i have been eating all day. other symptoms include excessive sweating during the night and over eating (im known by my family for eating alot) the exercise stops me gaining weight it would seem.