I have had Mononucleosis twice.
The first time I was in elementary school. Many of the symptoms are similar to those of Tuberculosis and upon an initial inspection, a doctor actually told my parents that it was possible that I may die. He then received the test results and apologized to my parents for scaring them half to death. It is rather easy to fight off as a young adult, but as a child, it can be rather serious. I was out of school for an entire month and was unable to walk or even get out of bed without assistance. I lost an unhealthy amount of weight and each time I would swallow food, it felt as if I was swallowing a ball too big for my throat, with spikes on it.
The second time I was in high school. I believe it was my Junior or Senior year. I was over it in about two weeks. Both of my parents were working, so I had to walk myself to the doctor after school and get myself checked out. When I explained to the doctor that I knew for a fact that I had Mono and was only coming to him to confirm my suspicion, he treated me as if I were an idiot, and explained to me that there is no way that I could know such a thing before being tested. Once he realized that I was correct, he offered me antibiotics which I of course refused.
The moral of the story is that Mono is a ***** when you are a kid, not too bad when you are a young adult, and that you should thank your lucky stars for that, and that apparantly the standards for getting in to medical school are very low these days.