Sick kid vs. sick adult

Why is it that a sick kid can still play, and be loud, just like when they are well? Even with a tremendous amount of snot running out of their nose and a cough. It boggles my mind. Ryan had the symptoms of a cold Friday night. Awesome because we had just been playing over a friend's house but I swear, he was fine. Not a drip from his nose or evena sneeze. He had a sneezing marathon in the tub and after that, it was full on cold. It was a matter of minutes. So, he stayed home with Ethan while I went to our playgroup anniversary luau on Saturday. He pretty much acts the same, running around like a maniac, but eats less. Sunday the cough started, but again he was about the same energy level. He woke up once in the night for medicine. I went to bed last night not feeling so hot and BAM, I am walking dead today. He is running circles around me. Its' 4:17....please Ethan come home early. I might be tied to a chair soon, and this poor kid needs some real food.