Anxiety is distinguished from fear, which is an appropriate cognitive and emotional response to a perceived threat. Anxiety is related to the specific behaviors of fight-or-flight responses, defensive behavior or escape. There is a false presumption that often circulates that anxiety only occurs in situations perceived as uncontrollable or unavoidable, but this is not always so. David Barlow defines anxiety as "a future-oriented mood state in which one is not ready or prepared to attempt to cope with upcoming negative events," and that it is a distinction between future and present dangers which divides anxiety and fear. Another description of anxiety is agony, dread, terror, or even apprehension. In positive psychology, anxiety is described as the mental state that results from a difficult challenge for which the subject has insufficient coping skills.

Fear and anxiety can be differentiated into four domains: (1) duration of emotional experience, (2) temporal focus, (3) specificity of the threat, and (4) motivated direction. Fear is short-lived, present-focused, geared towards a specific threat, and facilitating escape from threat. On the other hand, anxiety is long-acting, future-focused, broadly focused towards a diffuse threat, and promoting excessive caution while approaching a potential threat and interferes with constructive coping.

Joseph E. LeDoux and Lisa Feldman Barrett have both sought to separate automatic threat responses from additional associated cognitive activity within anxiety.

Anxiety can be experienced with long, drawn-out daily symptoms that reduce quality of life, known as chronic (or generalized) anxiety, or it can be experienced in short spurts with sporadic, stressful panic attacks, known as acute anxiety. Symptoms of anxiety can range in number, intensity, and frequency, depending on the person. However, most people do not suffer from chronic anxiety.

Anxiety can induce several psychological pains (e.g. depression) or mental disorders, and may lead to self-harm or suicide.

The behavioral effects of anxiety may include withdrawal from situations which have provoked anxiety or negative feelings in the past. Other effects may include changes in sleeping patterns, changes in habits, increase or decrease in food intake, and increased motor tension (such as foot tapping).

The emotional effects of anxiety may include feelings of apprehension or dread, trouble concentrating, feeling tense or jumpy, anticipating the worst, irritability, restlessness, watching for signs of danger, and a feeling of empty mindedness. as well as "nightmares/bad dreams, obsessions about sensations, déjà vu, a trapped-in-your-mind feeling, and feeling like everything is scary." It may include a vague experience and feeling of helplessness.

The cognitive effects of anxiety may include thoughts about suspected dangers, such as an irrational fear of dying or having a heart attack, when in reality all one is experiencing is mild chest pain, for example.

The physiological symptoms of anxiety may include:
• Neurological, as headache, paresthesias, fasciculations, vertigo, or presyncope.
• Digestive, as abdominal pain, nausea, diarrhea, indigestion, dry mouth, or bolus. Stress hormones released in an anxious state have an impact on bowel function and can manifest physical symptoms that may contribute to or exacerbate IBS.
• Respiratory, as shortness of breath or sighing breathing.
• Cardiac, as palpitations, tachycardia, or chest pain.
• Muscular, as fatigue, tremors, or tetany.
• Cutaneous, as perspiration, or itchy skin.
• Uro-genital, as frequent urination, urinary urgency, dyspareunia, or impotence, chronic pelvic pain syndrome.

There are various types of anxiety. Existential anxiety can occur when a person faces angst, an existential crisis, or nihilistic feelings. People can also face mathematical anxiety, somatic anxiety, stage fright, or test anxiety. Social anxiety refers to a fear of rejection and negative evaluation (being judged) by other people.
The philosopher Søren Kierkegaard, in The Concept of Anxiety (1844), 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), the 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.

The 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, the author of Man's Search for Meaning, when a person is 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.

Depending on the source of the threat, psychoanalytic theory distinguishes three types of anxiety: realistic, neurotic and moral.
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, the result is a decline in performance.

Test anxiety is the uneasiness, apprehension, or nervousness felt by students who have a fear of failing an exam. Students who have 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, uncontrollable crying or laughing 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. The DSM-IV classifies test anxiety as a type of social phobia.

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