Anxiety is an unpleasant emotional state characterized by extreme unease, apprehensiveness or fearfulness, the source of which may not be readily identifiable. Physiological effects of anxiety include increased heart rate, altered respiration rate, sweating, trembling, weakness and fatigue, psychological effects include feelings of impending danger, powerlessness, apprehension, and tension

Anxiety is probably the first emotion that a baby experiences, at the moment of birth and separation from the mother. In nearly all birds and mammals, an infant that is separated from the nest will show signs of intense anxiety, particularly by vocalizing

Anxiety is also a learned emotional response related to fear but differing from fear in that it tends to be of longer duration, of disproportionate intensity, more pervasive of the personality, and lacking a clear focus on an object. It also describes different degrees of susceptibility to fear. Highly anxious people are often considered to be neurotic introverts. It is more common in women than in men, and women are also more prone to psychiatric disturbances involving anxiety. While fear is a reaction to a real or threatening danger, anxiety is more typically a reaction to an unreal or imagined danger

Soren Kierkegaard regarded anxiety as intimately related to freedom. When a person confronts all the undetermined choices yet to be made in their life, their freedom, they properly become dizzy, or anxious. This anxiety is painful but necessary. If they react only to its pain, they draw back, and thus never quite become human. But if they see the worth of the freedom despite the pain, anxiety becomes a kind of tutor as they become human, use their creative powers, and confront life as it is. Paul Tillich distinguished between ontological anxiety, like Kierkegaard, and pathological anxiety

According to a USA report, anxiety disorders are the most costly group of mental illnesses. A 1990 study shows an estimated 46.6 billion dollars, about 32% of all US mental health costs, spent on the treatment of anxiety disorders

Entering the 21st century, levels of anxiety stand at record levels. People are not necessarily more miserable than they were fifty years ago, but they are certainly more anxious