24/03/2026
Fight or flight is a built-in survival response activated when the brain perceives threat, danger, or harm.
It begins in the amygdala, which detects the threat and signals the hypothalamus. This activates the HPA axis: the pituitary gland releases ACTH (adrenocorticotropic hormone), prompting the adrenal glands to release cortisol and adrenaline.
These hormones prepare the body for immediate action.
Physical responses may include:
Increased heart rate and blood pressure
Rapid breathing or air hunger
Muscle tension or shaking
Dilated pupils and tunnel vision
Flushed or pale skin
Dry mouth
Reduced digestion
Heightened alertness or, in some cases, auditory narrowing (difficulty processing sound clearly)
When the sympathetic nervous system remains activated, especially in trauma-related states, it can impact multiple body systems:
Cardiovascular: elevated heart rate, irregular rhythm, high blood pressure
Gastrointestinal: diarrhea, constipation, nausea, bloating
Urinary: urgency, frequency
Immune: increased susceptibility to infection, slower wound healing
Endocrine: blood sugar dysregulation, altered insulin response, hormonal imbalance
Sleep: insomnia, disrupted cycles, fatigue
Pain: increased sensitivity, chronic pain patterns
Neurological: headaches, dizziness, tinnitus, brain fog
Trauma responses can also affect cognition and behaviour:
Reduced concentration and memory recall
Difficulty learning or retaining information
Medication non-adherence
Avoidance of people, places, or care
Hypervigilance or emotional reactivity
Behavioural patterns that may emerge include:
Physical inactivity
Poor nutrition
Smoking or va**ng
Alcohol or substance use
Overeating or undereating
Compulsive behaviours (e.g. overworking, screen dependence)
There may also be an erosion of social connection:
Withdrawing from others
Reduced trust
Avoiding social environments
Difficulty maintaining relationships
Reluctance to seek or accept support
These responses are not flaws. They are adaptive survival mechanisms that can persist beyond the original threat.
Understanding the physiology behind them is key to supporting regulation, recovery, and long-term health outcomes.