Anxiety is 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.
Anxiety generally occurs without an identifiable triggering stimulus. As such, it is distinguished from fear, which occurs in the presence of an external 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.
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.
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 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 very basic of all human wishes is to find a meaning of life to combat this "trauma of nonbeing" as death is near and succumbing to it (even by suicide) seems attractive.
The "father" of existentialism, Søren Kierkegaard, regarded all humans to be born into despair by default (in The Sickness Unto Death). Such despair was created by having a false conception of the self. He regarded the mortal self which can exist relatively, and therefore be born or die, as the false self. The true self was the relationship of self to God, rather than to any relative object.
While the term "test anxiety" refers specifically to students, many adults 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.
"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.
It has been reported that patients with a significantly higher level of serum pseudocholinesterase experience greater frequency of anxiety. Pseudocholinestrase is a peripheral enzyme and may serve only as a marker rather than functional component of the problem.