Educational video describing the anatomy of the tensor fasciae latae muscle. Become a friend on facebook: http://www.facebook.com/drebraheim. Follow me on twitter: https://twitter.com/#!/DrEbraheim_UTMC. 1  Education. 2  Standard YouTube License.
The specific cause of body aches (myalgia) are the interleukins, which are primarily produced by the macrophages. These interleukins cause pain, body aches, hypersensitivity of the nerves, etc. Some of the interleukins (such as IL-2) cause the fever seen during the flu, and probably the headaches. Since these interleukins are produced in response many different kinds of bacterial and viral infections, symptoms such as fever, myalgia, and headaches can be seen in infections by many different etiologic agents.
Evolution rarely creates something from scratch, but rather, builds on existing foundations. So back to your question: Your chest hurts when you're emotionally sad because your brain processes physical and social pain in the same brain regions (dACC and AI) (the affective aspects of the pain).