What actually makes you feel sick? Discover how your immune system and proteins called cytokines respond to infections.br br --br br It starts with a tickle in your throat that becomes a cough. Your muscles begin to ache, you grow irritable, and you lose your appetite. It’s official: you’ve got the flu. It’s logical to assume that this miserable medley of symptoms is the result of the infection coursing through your body — but is that really the case? Marco A. Sotomayor explains what’s actually making you feel sick. br br Lesson by Marco A. Sotomayor, animation by Henrik Malmgren.