According to the trusty, but not so trustworthy, Internet, these little buggers are why my body has been aching all day long:
"Body aches are a side effect of the immune system response to an invading pathogen or germ. When your immune system detects the presence of these foreign objects, it uses certain proteins and chemicals (called cytokines) to communicate with the rest of the body. Some of these cytokines (like interleukins) can cause such things as fever and body aches, because they trigger these specific reactions."Uff da.