Anxiety is a generalized mood that can occur without an identifiable triggering stimulus. As such, it is distinguished from fear, which is an appropriate cognitive and emotional response to a perceived threat. Additionally, fear is related to the specific behaviors of escape and avoidance, whereas anxiety is related to situations perceived as uncontrollable or unavoidable.^[6] Another view defines anxiety as "a future-oriented mood state in which one is ready or prepared to attempt to cope with upcoming negative events,"^[7] suggesting that it is a distinction between future and present dangers which divides anxiety and fear. In a 2011 review of the literature,^[8] fear and anxiety were said to be differentiated in four domains: (1) duration of emotional experience, (2) temporal focus, (3) specificity of the threat, and (4) motivated direction. Fear was defined as short lived, present focused, geared towards a specific threat, and facilitating escape from threat; while anxiety was defined as long acting, future focused, broadly focused towards a diffuse threat, and promoting caution while approaching a potential threat.

Anxiety takes several forms: phobia, social anxiety, obsessive-compulsive, and post-traumatic stress.^[9] The physical effects of anxiety may include heart palpitations, tachycardia, muscle weakness and tension, fatigue, nausea, chest pain, shortness of breath, headache, stomach aches, or tension headaches. As the body prepares to deal with a threat, blood pressure, heart rate, perspiration, blood flow to the major muscle groups are increased, while immune and digestive functions are inhibited (the fight or flight response). External signs of anxiety may include pallor, sweating, trembling, and pupillary dilation. Someone who has anxiety might also experience it subjectively as a sense of dread or panic.^{[citation needed]}

Although panic attacks are not experienced by every person who has anxiety, they are a common symptom. Panic attacks usually come without warning and although the fear is generally irrational, the subjective 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 lose consciousness. Between panic attacks, people with panic disorder tend to suffer from anticipated anxiety- a fear of having a panic attack may lead to the development of phobias.^[10] Anxiety is the most common mental illness in America as approximately 40 million adults are affected by it.^[9]