easy child had mono 2 years ago and he had it bad. He missed tons of school, slept 16 hours of the day, yet refused to miss work. He was really angry with me the one day I called him off, but he looked horrible and, I thought, a bit yellow, and he was going to the doctor to be checked for jaundice (it's rare, but mono can affect the liver - though, more likely will the spleen). Mono ended up wiping out his immune system for months, so that even after he was over the mono he got every little thing that came along - except he was much more sick than everyone else with it.
I came down with it in December, 2005, and it was bad for 6 months.
Haozi - there is....ugh, can't find my words. Some people think it can come back, and some don't. It was thought that it was linked to Chronic Fatigue Syndrome, but the CDC has ruled that out. After my heart attack, I had a relapse (?) of Mono as found in a blood test, and I've read of it happening to others, but it is not considered common and many doctors don't think it can happen.