Alertness

Alertness is the state of active attention by high sensory awareness such as being watchful and prompt to meet danger or emergency, or being quick to perceive and act. It is related to psychology as well as to physiology. A lack of alertness is a symptom of a number of conditions, including narcolepsy, attention deficit disorder, chronic fatigue syndrome, depression, Addison's disease, or sleep deprivation. Pronounced lack of alertness can be graded as an altered level of consciousness. The word is formed from "alert", which comes from the Italian "all'erta" (on the watch, literally, on the height; 1618)

Physiological aspects

People who have to be alert during their jobs, such as air traffic controllers or pilots, often face challenges maintaining their alertness. Research shows that for people "...engaged in attention-intensive and monotonous tasks, retaining a constant level of alertness is rare if not impossible." If people employed in safety-related or transportation jobs have lapses in alertness, this "may lead to severe consequences in occupations ranging from air traffic control to monitoring of nuclear power plants."