Mononucleosis What is Mononucleosis? 1 What is Mononucleosis? Mononucleosis is a contagious viral disease which causes fatigue and malaise for a long time.This infectious condition may resolve on its own but requires lot of rest and self care to alleviate the symptoms. Mononucleosis: Why Am I So Tired?Have a question aboutMononucleosis?Ask a doctor now Expert AnswersCan a pathology report be wrong?Alcohol and Other Factors that Affect Recovery from...