adjective describes a noun as happening quickly and unexpectedly
adverb modifies a verb, adjective, or another adverb to describe how something is done
Sudden mood changes
Sudden cardiac arrest
Sudden death in sports
Sudden failure of a structure
Sudden thunderstorm
Sudden onset of symptoms
The sudden plot twist in the novel caught the readers by surprise.
The sudden onset of anxiety symptoms may require immediate intervention.
Emergency responders are trained to react quickly to sudden emergencies.
The sudden drop in stock prices was unexpected and required immediate analysis.
The sudden cardiac arrest of the patient required immediate resuscitation efforts.