COVID is sometimes viewed as two illnesses. The first in the outpatient setting presents somewhat as a flu but with some very different additional symptoms. The second is as the individual lapses into more difficult circumstances eventually involving a person's whole system.
"A cytokine storm, also called hypercytokinemia, is a physiological reaction in humans and other animals in which the innate immune system causes an uncontrolled and excessive release of pro-inflammatory signaling molecules called cytokines. Normally, cytokines are part of the body's immune response to infection, but their sudden release in large quantities can cause multisystem organ failure and death.[1] Cytokine storms can be caused by a number of infectious and non-infectious etiologies, especially viral respiratory infections such as H5N1 influenza, SARS-CoV-1,[2][3] and SARS-CoV-2 (COVID-19 agent). Other causative agents include the Epstein-Barr virus, cytomegalovirus, and group A streptococcus, and non-infectious conditions such as graft-versus-host disease.[4]"
https://en.wikipedia.org/wiki/Cytokine_storm
