The illness is unpredictable. Many people never have to be bedridden because their illness is so mild. Some people apparently have mono and recover without knowing they ever had it. Loss of energy Fatigue may be a factor in the recovery period. How long you remain tired from this illness varies considerably.
Many people have little or no fatigue at any time.
A few people will be tired for many months. Some will be somewhat tired for one to four weeks following a few days of fever at the beginning of their illness, gradually recovering their full strength and energy. Note that the fatigue is not the cause of the infectious mononucleosis but is the result of it. When a person becomes tired a few months after having mono, it is often impossible to decide whether it is from the mononucleosis itself or from some other cause. Certainly, those who have tend to be tired off and on before mono are not likely to be less tired afterwards.