The worst illnesses I think I've had have been pneumonia, strep throat, sinus infection, and (worst of all) mononucleosis (aka "mono"). Mono is terrible; you're tired all the time and you have a sore throat and your glands swell up a lot. Worst part is, it's contagious for 6 months, and your glands still swell up at inopportune times after. In fact, mine are swollen right now. If you want to avoid it, be careful who you share that soda with.