2. Extreme fatigue
Another highly common symptom of mono is fatigue. The fatigue can become so overwhelming that an infected person may not have the energy to perform even the simplest tasks. If you have mono, you may want to do little more than sleep.
And, no matter how much sleep you get, it is likely that you will still feel extremely tired. Since your immune system is working in overdrive to try and fight the virus, your energy can be severely drained. Fatigue can last for several days or weeks, and in extreme cases, it can last for several months.
