Sickness Behavior
Although the term "sickness behavior" may sound ambiguous, it actually kind of has to be. It's a catch-all phrase for that difficult-to-explain sensation that you get when you're sick. Everything we've already discussed is involved, as is how you respond to it when it actually occurs. You feel sluggish, unclean, worn out, and exhausted. Whichever illness you have, how you choose to handle it depends on wholly on you, refraining from moving or doing anything else. Stop infecting others, stop overworking yourself, and just concentrate on getting better.
Your sickness behavior and the array of dreadful symptoms you experience while you're unwell are caused by cytokines and other proteins. And while we've discussed some of the roles of some of the particular objects, the overall sense of awfulness appears to exist as a means of separation and preservation. To restrain oneself from getting up and doing anything else makes you feel terrible, essentially a form of self-quarantine. Stop infecting others, stop overworking yourself, and just concentrate on getting better.