If you have already gotten sick this winter season, you can attest to the fact that being sick is stressful, exhausting, and a downer. It is not a coincidence that when you are physically ill, you feel more depressed than usual. Medical illnesses like the flu or the common cold can closely mimic and cause depressive symptoms by activating your immune response and inflammation in your body.
Our immune, neurologic, and psychological systems are closely intertwined. When there is a foreign invader in your body, like the influenza virus, your cells produce proinflammatory cytokines, non-antibody proteins that activate and organize your body’s immune response (Raison 2006). These chemical proteins circulate throughout your body and communicate with your brain, which in turn produces its own cytokines. These brain cytokines lead to fever, fatigue, depressed mood, lack of appetite, lack of motivation, social withdrawal, poor concentration, and altered sleeping patterns. In other words, the physical sickness caused by the inflammatory response significantly overlaps with depressive symptoms.
Read more here on my Psych Today article.