What common symptom often indicates a viral infection?

Fatigue is a common symptom associated with viral infections due to the body's immune response. When a virus invades the body, the immune system activates to fight off the infection, which can lead to increased energy expenditure. This immune response often results in symptoms such as fever and muscle aches, both of which contribute to a feeling of fatigue. In contrast, conditions like increased appetite, weight gain, or elevated blood pressure are not typical indicators of a viral infection. Instead, they may be associated with other health issues or lifestyle factors. Thus, fatigue stands out as a key symptom commonly experienced during viral infections.