Anxiety Symptoms: What They Are And Why They Happen
Psychology Tools
Published
25 Feb 2026
Symptoms of anxiety can be confusing, alarming, and sometimes overwhelming. For many people, the physical symptoms of anxiety, such as a racing heart, dizziness, muscle tension, or shortness of breath, feel as though something is seriously wrong.
But why does anxiety happen? Many anxiety symptoms are the result of the body’s normal survival system that has evolved to help human beings respond to threats.
Understanding what anxiety symptoms are, how they affect the body and mind, and why they can become problematic can be an important part of psychological formulation and treatment.
This article explores the nature of anxiety symptoms, the role of the fight-or-flight response, and why anxiety can become persistent in certain conditions, such as panic disorder, generalized anxiety disorder (GAD), health anxiety, and phobias.
What are anxiety symptoms?
Anxiety is a natural response to things that we find threatening.
These threats might be physical, like accidents or violence; social, such as rejection or humiliation; or mental, including the possibility of losing control of your mind.
If anxiety becomes excessive, frequent, long-lasting, or begins to interfere with daily life, it can contribute to psychological difficulties such as panic disorder, generalized anxiety disorder, health anxiety, and phobias.
People experiencing anxiety may notice:
Nervousness, fear, apprehension, or worry.
Difficulty relaxing or sleeping.
Restlessness.
Tense muscles.
Fatigue.
Racing thoughts.
Difficulty concentrating.
Increased awareness of bodily sensations.
Why does anxiety happen? The fight-or-flight response
What triggers anxiety? Many anxiety symptoms can be understood through the body’s threat or ‘fight or flight’ response system.
An automatic physiological reaction to an event that is perceived as stressful or frightening, the fight or flight response prepares the body to fight or flee. It's the perception of threat that activates the sympathetic nervous system and triggers this acute stress response.
These responses are evolutionary adaptations that increase the chances of survival in threatening situations.
When the fight or flight response is activated, a chain reaction occurs throughout the body. It includes the following:
Changes in heart rate and circulation
What changes:
Increased heart rate
Increased blood flow
Dilation of the coronary blood vessels
Blood vessels serving muscles also dilate
Blood vessels serving the digestive system constrict
Why does this happen? These changes increase the availability of oxygen and energy to the heart and skeletal muscles and redirect blood flow toward muscles and the brain.
Changes in breathing
What changes:
Dilation of the bronchi
Increased respiration rate
Why does this happen? Quicker breathing takes in more oxygen to power the muscles. This makes the body more able to fight or run away.
Changes in energy availability
What happens:
Increased conversion of glycogen to glucose
Why does this happen? This increases the availability of glucose in skeletal muscle and brain cells.
Changes in vision and attention
What changes:
Dilation of the pupils
Vision can become acute so that more attention can be paid to danger. Some people notice “tunnel vision” or that their vision becomes “sharper”
Why does this happen? Automatic reactions include a quickening of thought and an attentional focus on salient targets, including the source of the threat and potential avenues for escape.
Changes in muscles and the digestive system
What changes:
Muscles all over the body tense so they are prepared
Muscles may also shake or tremble, so they are ready for action
Why does this happen? Digestion shuts down as energy is diverted toward the muscles. Blood is diverted away from the digestive system, which can lead to feelings of nausea or “butterflies”.
These physical changes are adaptive responses to perceived threats. However, in many anxiety disorders, it isn’t the sensations themselves that become problematic, but the meaning people assign to them.
Why the physical symptoms of anxiety can feel dangerous
Anxiety symptoms often become distressing, not because they are dangerous, but because they are misinterpreted as dangerous.
For example, someone with panic disorder might misinterpret fight or flight responses as signs that something terrible is about to happen, such as:
“I’m having a heart attack.”
“If this carries on, I’ll go mad.”
People who panic also tend to think in biased ways at times, such as catastrophizing (assuming that the worst scenario is bound to happen) and fortune-telling (jumping to negative conclusions about what is going to occur in the future). These interpretations are likely to increase fear, which in turn increases anxiety symptoms.
How anxiety can become a vicious cycle
Anxiety symptoms do not occur in isolation.
Thoughts, emotions, body sensations, and behaviors all interact with one another.
Take panic attacks, for example. A panic attack often begins with a trigger. This could be a particular situation or bodily sensation. If this experience is interpreted in a threatening way, fear increases and activates the fight-flight-freeze response. Changes in breathing, heart rate, sweating, and muscle tension then follow.
These body sensations may be interpreted as dangerous (e.g., “My heart is racing – that must mean that I’m going to have a heart attack”) and can, unfortunately, lead to more fear, more physical sensations, and more anxious interpretations.
In this way, a vicious cycle forms in which anxious thoughts lead to anxious emotions, which lead to anxious body sensations, which lead to more anxious thoughts about those sensations and their consequences.
Anxiety symptoms across different anxiety problems
The same physiological systems are involved in many anxiety disorders, but the way symptoms are interpreted and maintained can vary. The following examples illustrate how anxiety symptoms present in several common anxiety disorders.
Panic disorder
People with panic disorder experience sudden and repeated attacks of fear accompanied by strong physical reactions such as a racing heartbeat, sweating, shaking, and thoughts that something terrible is happening or will happen.
They often worry about future panic attacks and may avoid places where panic has occurred before.
Generalized anxiety disorder (GAD)
The main symptom of GAD is excessive worry. Worry is a chain of thoughts and images that can progress in ever more catastrophic and unlikely directions.
For example, an individual with GAD may worry about what might happen to them or the people they care about. These worries often chain together into increasingly catastrophic scenarios about their health, relationships, work, finances, or the future.
Health anxiety
People with health anxiety may be worried about having, developing, or catching a serious illness. They may repeatedly check their bodies for signs of illness, seek reassurance, research health concerns, and remain unconvinced by negative test results.
Phobias
Phobias are intense fears that are triggered by specific objects or situations – fear which is out of proportion to the actual danger. People with a phobia may avoid the thing that scares them, worry about encountering it in the future, and believe that something terrible will happen if they do.
Considered together, these examples highlight several important principles that can help therapists explain anxiety symptoms to clients.
5 Key insights about anxiety symptoms worth sharing with clients
Anxiety is a survival response: The fight-flight-freeze response evolved to help human beings survive danger by preparing the body for action.
Symptoms are normal and have a purpose: A faster heartbeat, quicker breathing, muscle tension, sweating, and increased attention all serve functions designed to improve survival during threat.
Physical symptoms of anxiety are frequently misinterpreted: Many anxiety difficulties are maintained when normal bodily sensations are interpreted as signs of a catastrophe.
Attention matters: When people feel anxious, they tend to focus on signs of danger, illness, or anxiety symptoms. As a result, they are more likely to notice these things.
Playing it safe can maintain anxiety: Avoidance and ‘safety behaviors’ (actions or inactions that aim to increase one’s sense of safety) can prevent people from learning how dangerous a situation truly is, or what they are capable of coping with.
Together, these principles provide a framework for understanding why anxiety symptoms occur, why they can become persistent, and how they can be addressed in therapy.
If you’re looking to apply these principles in practice, Psychology Tools offers a comprehensive library of anxiety resources to support clinical practice. From psychoeducation and CBT formulations to worksheets and treatment resources, these materials can help therapists explain anxiety symptoms, develop shared formulations with clients, and guide evidence-based interventions.
Conclusion
The physical symptoms of anxiety can be frightening, particularly when they are intense, unexpected, or unfamiliar.
However, many of the sensations associated with anxiety are the result of normal biological systems designed to protect us from danger. Understanding the fight-or-flight response, the role of thoughts and interpretations, and the factors that maintain anxiety can help clients make sense of their anxiety symptoms, whether they occur in the context of panic disorder, generalized anxiety disorder, health anxiety, or phobias.
Rather than being a random or meaningless experience, symptoms of anxiety are an understandable response that is shaped by many factors, including evolution, attention, interpretation, and behavior.
Understanding anxiety symptoms in this way helps clinicians move beyond viewing them as isolated experiences. Instead, symptoms can be understood as part of an interconnected system involving threat perception, physiological responses, cognitive interpretations, attention, and behavior. This formulation provides a foundation for helping clients make sense of their experiences and informs cognitive behavioral interventions that target the processes maintaining anxiety.
Further reading
Cannon, W. B. (1915). Bodily changes in pain, hunger, fear, and rage. New York: Appleton-Century-Crofts.
Schauer, M., & Elbert, T. (2010). Dissociation following traumatic stress. Journal of Psychology, 218, 109–127.
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