"Exacerbation" primarily means "A bad situation made worse." A sentence accurately using the word "exacerbation" would be, "The sick man's family feared an exacerbation of his illness."
"Exacerbation" is a noun referring to a situation, confrontation, disease, injury or relationship that is made more difficult by actions or circumstance. It can also be a synonym for "irritate" or "exasperate." It is derived from Latin and shares a root with "acerbate," meaning "to make sour or bitter."
It has a particular definition within the context of Chronic Obstructive Pulmonary Disease. An exacerbation of COPD is a sometimes-unexplained worsening flare up of the illness that further disrupts a patient's ability to breathe.