|Classification and external resources|
A marble bust of the Roman Emperor Decius from the Capitoline Museum. This portrait "conveys an impression of anxiety and weariness, as of a man shouldering heavy [state] responsibilities." 
Anxiety is a psychological and physiological state characterized by cognitive, somatic, emotional, and behavioral components. These components combine to create an unpleasant feeling that is typically associated with uneasiness, apprehension, fear, or worry. Anxiety is a generalized mood condition that can often occur without an identifiable triggering stimulus. As such, it is distinguished from fear, which occurs in the presence of an observed threat. Additionally, fear is related to the specific behaviors of escape and avoidance, whereas anxiety is the result of threats that are perceived to be uncontrollable or unavoidable.
Another view is that anxiety is "a future-oriented mood state in which one is ready or prepared to attempt to cope with upcoming negative events" suggesting that it is a distinction between future vs. present dangers that divides anxiety and fear. Anxiety is considered to be a normal reaction to stress. It may help a person to deal with a difficult situation, for example at work or at school, by prompting one to cope with it. When anxiety becomes excessive, it may fall under the classification of an anxiety disorder.
Physical effects of anxiety may include heart palpitations, muscle weakness and tension, fatigue, nausea, chest pain, shortness of breath, stomach aches, or headaches. The body prepares to deal with a threat: blood pressure and heart rate are increased, sweating is increased, bloodflow to the major muscle groups is increased, and immune and digestive system functions are inhibited (the fight or flight response). External signs of anxiety may include pale skin, sweating, trembling, and pupillary dilation. Someone suffering from anxiety might also experience it as a sense of dread or panic. Although panic attacks are not experienced by every anxiety sufferer, they are a common symptom. Panic attacks usually come without warning, and although the fear is generally irrational, the perception of danger is very real. A person experiencing a panic attack will often feel as if he or she is about to die or pass out. Panic attacks may be confused with heart attacks therefore only a doctor can differentiate between a panic attack or a heart attack.
Anxiety does not only consist of physical effects; there are many emotional ones as well. They include "feelings of apprehension or dread, trouble concentrating, feeling tense or jumpy, anticipating the worst, irritability, restlessness, watching (and waiting) for signs (and occurrences) or danger, and, feeling like your mind's gone blank" as well as "nightmares/bad dreams, obsessions about sensations, deja vu, a trapped in your mind feeling, and feeling like everything is scary."
Cognitive effects of anxiety may include thoughts about suspected dangers, such as fear of dying. "You may...fear that the chest pains [a physical symptom of anxiety] are a deadly heart attack or that the shooting pains in your head [another physical symptom of anxiety] are the result of a tumor or aneurysm. You feel an intense fear when you think of dying, or you may think of it more often than normal, or can’t get it out of your mind."
Neural circuitry involving the amygdala and hippocampus is thought to underlie anxiety. When confronted with unpleasant and potentially harmful stimuli such as foul odors or tastes, PET-scans show increased bloodflow in the amygdala. In these studies, the participants also reported moderate anxiety. This might indicate that anxiety is a protective mechanism designed to prevent the organism from engaging in potentially harmful behaviors.
Research upon adolescents that were as infants highly apprehensive, vigilant, and fearful finds that their nucleus accumbens is more sensitive than that in other people when they selected to make an action that determined whether they received a reward. This suggests a link between circuits responsible for fear and also reward in anxious people. As researchers note "a sense of ‘responsibility,’ or self agency, in a context of uncertainty (probabilistic outcomes) drives the neural system underlying appetitive motivation (i.e., nucleus accumbens) more strongly in temperamentally inhibited than noninhibited adolescents."
Although single genes have little effect on complex traits and interact heavily both between themselves and with the external factors, research is underway to unravel possible molecular mechanisms underlying anxiety and comorbid conditions. One candidate gene with polymorphisms that influence anxiety is PLXNA2.
Pre-existing health issues including chronic obstructive pulmonary disease (COPD), heart failure, and arrythmia can be the cause of anxiety or anxiety symptoms
The HAM-A (Hamilton Anxiety Scale)  is a widely used interview scale that measures the severity of a patient's anxiety, based on 14 parameters, including anxious mood, tension, fears, insomnia, somatic complaints and behavior at the interview. Developed by M. Hamilton in 1959, the scale predates the current definition of generalized anxiety disorder (GAD). However, it covers many of the features of GAD and can be helpful in assessing its severity.
Philosopher Søren Kierkegaard, in The Concept of Anxiety, described anxiety or dread associated with the "dizziness of freedom" and suggested the possibility for positive resolution of anxiety through the self-conscious exercise of responsibility and choosing. In Art and Artist (1932), psychologist Otto Rank wrote that the psychological trauma of birth was the pre-eminent human symbol of existential anxiety and encompasses the creative person's simultaneous fear of--and desire for--separation, individuation and differentiation.
Theologian Paul Tillich characterized existential anxiety as "the state in which a being is aware of its possible nonbeing" and he listed three categories for the nonbeing and resulting anxiety: ontic (fate and death), moral (guilt and condemnation), and spiritual (emptiness and meaninglessness). According to Tillich, the last of these three types of existential anxiety, i.e. spiritual anxiety, is predominant in modern times while the others were predominant in earlier periods. Tillich argues that this anxiety can be accepted as part of the human condition or it can be resisted but with negative consequences. In its pathological form, spiritual anxiety may tend to "drive the person toward the creation of certitude in systems of meaning which are supported by tradition and authority" even though such "undoubted certitude is not built on the rock of reality".
According to Viktor Frankl, author of Man's Search for Meaning, when faced with extreme mortal dangers the most basic of all human wishes is to find a meaning of life to combat the "trauma of nonbeing" as death is near.
According to Yerkes-Dodson law, an optimal level of arousal is necessary to best complete a task such as an exam, performance, or competitive event. However, when the anxiety or level of arousal exceeds that optimum, it results in a decline in performance.
Test anxiety is the uneasiness, apprehension, or nervousness felt by students who had a fear of failing an exam. Students suffering from test anxiety may experience any of the following: the association of grades with personal worth, fear of embarrassment by a teacher, fear of alienation from parents or friends, time pressures, or feeling a loss of control. Sweating, dizziness, headaches, racing heartbeats, nausea, fidgeting, and drumming on a desk are all common. Because test anxiety hinges on fear of negative evaluation, debate exists as to whether test anxiety is itself a unique anxiety disorder or whether it is a specific type of social phobia.
While the term "test anxiety" refers specifically to students, many workers share the same experience with regard to their career or profession. The fear of failing a task and being negatively evaluated for it can have a similarly negative effect on the adult.
Anxiety when meeting or interacting with unknown people is a common stage of development in young people. For others, it may persist into adulthood and become social anxiety or social phobia. "Stranger anxiety" in small children is not a phobia. Rather it is a developmentally appropriate fear by toddlers and preschool children of those who are not parents or family members. In adults, an excessive fear of other people is not a developmentally common stage; it is called social anxiety.
Anxiety can be either a short term 'state' or a long term "trait." Trait anxiety reflects a stable tendency to respond with state anxiety in the anticipation of threatening situations. It is closely related to the personality trait of neuroticism.
"Today we’re all faced with greater choice, more competition and less time to consider our options or seek out the right advice."
Paradoxical anxiety is anxiety arising from use of methods or techniques which are normally used to reduce anxiety. This includes relaxation or meditation techniques as well as use of certain medications. In some buddhist meditation literature, this effect, although it is not referred to as anxiety there due to the religious context of the writing, is described as something which arises naturally and should be turned toward and mindfully explored in order to gain insight into the nature of emotion, and more profoundly, the nature of self.
Anxiety is a physiological state characterized by cognitive, somatic, emotional, and behavioral components (Seligman, Walker & Rosenhan, 2001). These components combine to create the feelings that we typically recognize as fear, apprehension, or worry. Anxiety is often accompanied by physical sensations such as heart palpitations, nausea, chest pain, shortness of breath, stomach aches, or headache. The cognitive component entails expectation of a diffuse and certain danger.
Anxiety is a vague, unpleasant emotional state which is characterised by experiences of apprehension, dread, distress, and uneasiness.