Stuck in Fight-or-Flight? Understanding Vagal Tone

Many chronic symptoms people experience today — digestive issues, fatigue, anxiety, poor sleep, and inflammation — are not isolated problems. They are often signs of a nervous system that has become stuck in sympathetic dominance, also known as “fight or flight.”  A key player in restoring balance is vagal tone, which reflects how well your vagus nerve helps shift your body into the parasympathetic state — the mode responsible for rest, digestion, repair, and healing.  When vagal tone is strong, the body adapts to stress efficiently. When vagal tone is weak, the body stays in survival mode, even when danger has passed.

Why the Gut and Nervous System Are Deeply Connected

The vagus nerve serves as the main communication highway between the brain and the gastrointestinal (GI) tract. In fact, most signals travel from the gut to the brain, meaning digestive health strongly influences mood, stress tolerance, and energy levels.

When vagal tone is reduced, digestion often slows and becomes less efficient. This may lead to:

• Low stomach acid
• Bloating or reflux
• Constipation or IBS symptoms
• Microbiome imbalance
• Increased intestinal inflammation

Inflammation in the gut then sends distress signals back to the brain, reinforcing stress physiology and keeping the nervous system activated. Over time, this creates a cycle where stress worsens digestion, and poor digestion worsens stress.

Common Signs of Sympathetic Dominance

When your body maintains sympathetic dominance, you may notice:

• Feeling tired but unable to relax
• Anxiety or heightened stress sensitivity
• Brain fog or poor focus
• Sleep difficulties
• Food sensitivities
• Heart palpitations or dizziness
• Slow recovery from illness or exercise
• Persistent digestive discomfort

Hidden Triggers That Keep You Stuck in Sympathetic Dominance

Emotional stress is only one piece of the puzzle. Many people remain stuck in fight-or-flight because of ongoing biological stressors, the most common including:

• Chronic psychological stress or trauma
• Poor sleep and circadian disruption
• Blood sugar instability
• Gut infections or dysbiosis
• Excess caffeine or overtraining
• Chronic pain or inflammation

In our Functional Medicine practice, we also recognize less obvious triggers that can continuously stimulate the immune and nervous systems which include:

• Mold or mycotoxin exposure from water-damaged buildings and certain foods
• Stealth or chronic infections such as viruses, Lyme disease and other tick-borne infections affecting autonomic regulation

Heart Rate Variability (HRV): A Simple Way to Measure Nervous System Health

Heart Rate Variability (HRV) measures the variation between heartbeats and provides insight into nervous system flexibility between fight or flight (sympathetic) and rest, heal, and digest (parasympathetic).

Higher HRV generally reflects stronger vagal tone and resilience. Lower HRV often indicates sympathetic dominance and reduced recovery capacity.

There are many options to measure HRV, including high-accuracy chest straps, smart rings, fitness bands, and advanced smartwatches. These tools are called monitors, sensors, or trackers and utilize an electrocardiogram (ECG)  for precision or photoplethysmography (PPG) for 24/7 tracking.  For the best measurement results, measure in the morning before caffeine or activity, and track trends over time rather than focusing on a single measurement.

How to Strengthen Vagal Tone

Healing the nervous system involves both removing triggers and actively supporting regulation.  Helpful daily practices to stop sympathetic dominance (fight or flight) and improve vagal tone include:

• Slow diaphragmatic breathing to stimulate vagal activation
• Meditation, prayer, humming, gargling, or singing to activate vagal pathways
• Supporting gut health with whole foods, fiber, and adequate protein
• Addressing underlying drivers such as mold exposure, infections, or inflammation
• Physical activity such as walking or moderate aerobic exercise
• Consistent sleep timing and morning sunlight exposure
• Meaningful social connection and positive emotional experiences
• Devices called “vagus nerve stimulators” -you can find several available online

Strengthening vagal tone helps restore communication between the brain, gut, immune system, and heart — allowing the body to shift from survival mode back into healing.  Small, consistent changes practiced daily often create the greatest improvements. As nervous system balance returns, many people experience calmer moods, improved digestion, deeper sleep, and greater resilience to stress.

Be at peace. Be well.

References

• Tracey KJ. The inflammatory reflex. Nature. 2002.
• Bonaz B et al. Microbiota–gut–brain axis and vagal function. Frontiers in Neuroscience. 2018.
• Shaffer F & Ginsberg JP. Heart rate variability metrics and norms. Frontiers in Public Health. 2017.
• Proal AD & VanElzakker MB. Post-viral mechanisms and Long COVID. Frontiers in Immunology. 2021.
• Brewer JH et al. Mold exposure and inflammatory illness. Toxins. 2013.
• Novak P. Autonomic dysfunction in Lyme disease. Clinical Autonomic Research. 2016.

The Woodlands Institute for Health & Wellness - Mila McManus MD

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