Why does having a cold drain you so?

Having a cold drains you because your immune system is actively working to fight off the viral infection, which requires significant energy and resources. Symptoms like fever, congestion, and fatigue are the body's responses to the virus, diverting energy away from other functions. Additionally, the inflammation caused by the immune response can lead to overall malaise and weakness. This combination of factors can leave you feeling exhausted even with minimal physical exertion.