The medical community is not sure why the symptoms arise. Some experts believe that it may be due to the lingering effects of the virus as the body continues to clear it out.One theory is that the virus overloads the immune system, causing a reaction that triggers symptoms.An earlier study suggest that the symptom of fatigue after a viral infection is due to inflammation in the brain.Viruses cause the immune system to respond and attack them. This response causes stress and inflammation in the body. The effects of this response often leave people feeling down, fatigued, and sometimes depressed. a viral infection essentially forces your immune system to remain in the “on” position. This causes a shift in the homeostasis of your immune system, and never really allows your immune system to rest or reset. Because the immune system requires massive amounts of energy to function, this leaves your body energy-depleted and causes fatigue symptoms.And in the wake of 2020’s coronavirus pandemic, some speculate that we may be facing a massive wave of new cases of chronic fatigue syndrome.