I'm no doctor, but i had the mono in Jan. 05. For me, I had two blood test done. One was from my University Student Health Services and the other From the local Hospital. Oh, by the way, i had a severe case of Mono. I went into the hospital for some abdominal pain. It turned out to be nothing the first time around, but they did blood test to confirm I had mono; they gave me some fluids via IV and then sent me on my way.
As I as I said my case of mono was severe. I experienced the fatigue big time. I was tired alot; sleeping 12+ hours the first week that I had. It really hindered me taking classes (Engineerig undergrad here). I went to the hospital, again, Midnight of the 9th day i was officaly Diagnosed with mono. Mind you, I lost my appetite for all food. Granted it was college food. I was drinking gatorade annd other engergy drinks, but even then i sometimes couldn't keep the fluid down.
So, as I said, I went into the hospital at Midnight, 8 hrs later I was on the opertating room b/c my enlarged spleen(got bigger b/c of the mono) ruptured and I was bleeding internally. I lost 1.5 liters of blood. And believe me, I did my best to stay rested and not do any physical activity.
So, If you have mono, take it easy; get some rest. Remember, mono can kill, b/c it almost got me.