The Physical Symptoms of Anxiety: The Fight and Flight Response
Updated: Sep 4
Demystifying the Physical Symptoms of Anxiety
Anxiety can produce very real physical sensations: a racing heart, dizziness, sweating, trembling, nausea, tightness in the chest or a feeling that something terrible is about to happen.
Understanding why the body responds in this way can make these sensations feel less mysterious.
Our Threat Response
Human beings have evolved systems that help us respond rapidly to possible danger.
When the brain detects a threat, the body can prepare for action. This is often described as the fight-or-flight response, although defensive responses can also include freezing or becoming more vigilant.
These responses would have been particularly useful when our ancestors faced immediate physical threats. If danger appeared, quickly mobilising energy, increasing alertness and preparing the muscles for action could improve the chances of escaping or defending ourselves.
The same basic threat systems remain with us today.
What Happens in the Brain?
There is no single “fear centre” in the brain.
Instead, several interconnected brain systems are involved in detecting and learning about threat, interpreting what is happening and coordinating the body's response.
The amygdala plays an important role in recognising and learning about potentially threatening information, but it works alongside areas including the hippocampus, prefrontal cortex and insula.
Importantly, threat responses can begin very quickly. We do not always have to make a deliberate, conscious decision that something is dangerous before our body reacts.
This is useful: if we had to carefully analyse every possible danger before responding, we might sometimes respond too slowly.
What Happens in the Body?
When the threat system becomes activated, the sympathetic nervous system helps prepare the body for action.
Our heart rate may increase, our breathing may become faster, our muscles may tense and we may begin to sweat. Hormones including adrenaline help mobilise energy so that the body is ready to respond.
At the same time, processes that are less immediately important may change. Digestion, for example, can be affected, which is one reason anxiety may produce nausea, stomach discomfort or “butterflies”.
Breathing can also change. Some people begin to breathe faster or more deeply than their body requires. This can reduce carbon dioxide levels in the blood and temporarily alter blood flow to the brain, contributing to sensations such as dizziness, tingling, light-headedness or feeling detached.
Although these sensations can feel alarming, they are common features of anxiety.
Why Does the Alarm Sometimes Go Off When We Are Safe?
One useful way of understanding anxiety from an evolutionary perspective is to think of the threat system as being rather like a sensitive smoke alarm.
For our ancestors, failing to respond to genuine danger could carry a very high cost. Responding unnecessarily was often much less costly.
Evolution would therefore favour a system that sometimes produced a false alarm rather than one that regularly failed to respond to real danger.
Modern anxiety can work in a similar way.
Our threat system does not respond only to immediate physical danger. It can also react to uncertainty, memories, imagined future events and social threats.
What About Social Anxiety?
For humans, relationships with other people have always mattered.
Throughout our evolutionary history, belonging to a group provided access to protection, cooperation, resources and support. Social rejection, exclusion and loss of status could therefore carry significant consequences.
It makes sense that humans developed a strong sensitivity to signs that our relationships or social standing might be threatened.
Today, this system can become activated in situations such as:
speaking in front of other people
meeting someone new
being criticised
worrying about making a mistake
feeling judged
experiencing rejection
believing that we have embarrassed ourselves.
There may be no immediate physical danger, but our brain can still interpret the situation as important enough to activate a threat response.
Culture, previous experiences and learning also influence the situations in which we experience shame, embarrassment or social threat.
Why Understanding This Can Help
The physical symptoms of anxiety are therefore not random.
They arise from systems designed to protect us.
Sometimes those systems respond appropriately to danger. At other times, the alarm is triggered when the situation is uncomfortable or uncertain rather than genuinely dangerous.
Understanding this distinction can be important in therapy. Rather than treating the physical sensations themselves as evidence that something terrible is happening, we can begin to recognise them as part of an activated threat system.
With practice, we can learn to respond differently to both the sensations and the situations that trigger them.
