Living in Fight-or-Flight: What Can Actually Be Measured

Georgina Waugh, Clinical Nutritionist (BHSc Nutritional Medicine) · 9 minute read · Updated 25 October 2026

If you've ever googled "why am I wired but tired" at 11pm, you already know the feeling. Buzzing when you should be winding down. Flat and exhausted when you should be waking up. Agitated and irritable over things that never used to bother you.

A lot of the time, what's happening is that your body is stuck in "fight-or-flight". Your stress hormones keep running as if there's a threat to deal with, long after the threat is gone, or even when there never was one.

So let's talk about what living in fight-or-flight actually looks like in the body, what can be measured, and what I'd check first if you sat down in my clinic.

The short version

• Being stuck in fight/flight mode describes a real pattern of nervous system dysfunction, where stress hormones like cortisol and adrenaline stay switched on. It isn't a diagnosis, and not many tests can 100% confirm this heightened nervous system response.
• Low iron, an underactive thyroid, sleep apnoea, perimenopause and anxiety all produce the same symptoms. Those can be tested for, so that should be done first.
• What can be measured is how your stress response is running: the shape of your cortisol across the day, and your heart rate variability compared with your own baseline.
• The order matters. First two weeks of notes, then GP bloods, then a sleep check, and then the cortisol testing. If you skip straight to the end, you get a cortisol report and still no answers about the "why" behind the cortisol dysregulation.

Why does it feel like everyone is in fight/flight right now?

A few years ago you'd rarely hear anyone outside a psychology clinic talking about their nervous system. Now it's a whole corner of the internet: cold plunges, saunas, breathing patterns, mouth tape, red light, Oura rings, gadgets for your vagus nerve, all promising to get you out of fight/flight mode.

Psychologists at UC San Diego have written about this trend, and I think their take is fair. Nervous system language feels a lot kinder than "I can't cope", and it recognises that what you're feeling is physical, not all in your head.

What's actually happening when you're stuck in fight-or-flight

Your autonomic nervous system runs everything you don't have to think about: heart rate, breathing, digestion and the release of stress hormones.

It has two modes that are meant to take turns across the day. One is the accelerator, your sympathetic "fight-or-flight" response. It releases adrenaline and cortisol, raises your heart rate, sends blood to your muscles and puts digestion and repair on hold. The other is the brake, your "rest and digest" mode, where your body recovers, digests and repairs.

In a body that's coping, the accelerator kicks in for a deadline or a near miss on the freeway, then switches off again once it's passed. Cortisol rises sharply in the first half hour after you wake, gradually falls through the day and is at its lowest around midnight.

When your nervous system isn't working the way it should, the accelerator never fully switches off. Stress hormones stay higher than they should for longer, and the natural rhythm gets out of whack. That can look like dragging yourself out of bed in the morning, your brain switching on and racing when you wake between 2 and 4am, your heart pounding over an email or a menstrual cycle shifting.

What gets measured is the shape of the curve, not a single number. On a typical day, cortisol rises sharply in the first 30 to 45 minutes after waking and is at its lowest around midnight. The flatter line, low in the morning and still raised at night, is the pattern of a body stuck in fight-or-flight. It looks the same whatever is driving it.

This is a real physiological state, and it's really common.

Two things fight/flight mode isn't

1. It isn't a diagnosis

No pathology lab in Australia offers a "stuck in fight-or-flight" test, because there's no agreed definition to test against.

A single cortisol reading on its own is a good example. It only shows what your body was doing at that one moment, so it tells us very little about how your stress hormones behave across the day.

2. It isn't proof that stress is the cause

This is the one that matters most in clinic.

Read the symptom list again: wired but exhausted, broken sleep, racing heart, brain fog, snapping at the people you love. Low iron can cause all of that. So can an underactive thyroid, undiagnosed sleep apnoea and perimenopause.

Your body treats running low on iron, oxygen or sleep as a threat. So a stress response that looks stuck in fight-or-flight on a saliva test is often doing exactly what it's meant to do in a body that's under-resourced.

The cortisol report is rarely the first thing I want to see. The last two years of bloods usually tell me more.

What I see in clinic. The client I see most often is a woman in her late thirties and forties who has done her bloods, been told "everything's normal", and has a long list of symptoms that she's been told are down to "her age" or "stress".

Her cortisol curve is flat, and that's useful information. But it's the third piece of the puzzle, and she's been handed it first. When we go back and run more thorough bloods, there's very often something in them that explains more than the cortisol curve does.

The stress hormone pattern is real and it's happening. It's just not where the story starts.

What can actually be measured, and the order I'd do it in

Each step rules something in or out before you spend money on the next one.

1. Write the pattern down for two weeks

Skip the app and just use the notes on your phone. Write down your bedtime, your wake time, whether you woke in the night and when, whether you had an afternoon crash, any caffeine after midday, any alcohol, and one word for how you felt.

Two weeks of this tells a practitioner more than most tests do, and it's free. If you're waking at 3am, note the exact time. Waking at the same hour every night is a different clue from randomly broken sleep.

2. GP bloods before any functional testing

A ferritin that's just inside the reference range can still be low for you.

If your pattern looks like	Ask your GP about	Why it's on the list
3am waking, heavy periods, breathless on stairs	Full blood examination, full thyroid panel and antibodies, iron studies including ferritin	Low iron stores can cause the whole fight-or-flight picture long before anaemia shows up
Flat, cold, foggy, weight creeping up	Full thyroid panel including antibodies, HbA1c/blood sugar, insulin and liver enzymes	An underactive thyroid looks almost exactly like a flat cortisol curve
Pins and needles, low mood, poor memory	Vitamin B12, folate, vitamin D	Common, cheap to check and easy to miss on a standard panel
Shaky by 11am, the 3pm crash, waking hungry	Fasting glucose or HbA1c, fasting insulin, iron studies	Blood sugar drops trigger a release of adrenaline and cortisol, so they feel exactly like a stress response
Snoring, waking unrefreshed most mornings, a partner who has noticed pauses in your breathing	A sleep study referral	Sleep apnoea is common and often missed in women, and no saliva test will pick it up

3. Sleep and breathing

If you snore, wake up unrefreshed most mornings, or your partner has noticed you stop breathing in your sleep, ask your GP about a sleep study before doing any stress testing. Every time your breathing stops, your body goes into fight-or-flight to wake you up enough to breathe again. That gives you the classic picture of high night-time cortisol, a racing heart in the morning and exhaustion that no amount of breathwork will fix.

4. Then your stress hormone rhythm

Once the common causes have been ruled in or out, two measurements show directly how your stress response is running.

Cortisol across the day. A single morning blood cortisol tells you almost nothing about your rhythm. What matters is the shape of the curve, so samples are taken when you wake, 30 to 45 minutes later, mid-afternoon and before bed, using saliva or dried urine at home. The 2016 expert consensus on measuring the morning cortisol rise is clear that timing is everything, which is why following the collection instructions matters more than which lab you use.

Heart rate variability (HRV). This is the small variation in time between your heartbeats. When fight-or-flight is dominant, HRV tends to drop, and when your body is in rest and digest, it tends to rise. Most watches and rings now track it. There are two caveats from the research. First, "normal" values vary enormously from person to person, so a number on its own means very little. Second, what's useful is your own trend over weeks. HRV dropping during a hard month and recovering once it's over tells you something. A single low reading doesn't.

What these tests can and can't tell you

Together, a cortisol curve and an HRV trend show a practitioner how hard your stress response is working and whether it's switching off when it should. That lets a consultation go well beyond "you seem stressed".

What they can't tell you is why. If a woman is iron deficient, sleeping five good quality hours a night and in early perimenopause, her flat cortisol curve has three possible explanations, and the test doesn't tell you which one matters most. That's the job of the practitioner reading it.

That's also why I don't often order cortisol testing first or on its own. There are plenty of other functional tests that give far more clinical insight than stress hormone testing alone.

What helps while you're finding out

None of this replaces the checks above. But your stress response responds to routine more than to any one trick, and these are the things I ask almost everyone to start with.

• Wake up at the same time seven days a week, and get daylight in the first half hour. Your morning cortisol rise is set by light and routine, and this is the cheapest thing you can do for it.
• Eat protein at breakfast, and have something to eat before the afternoon slump. Stable blood sugar means your body doesn't have to release adrenaline and cortisol to keep you going, and it's a better option than a 3pm coffee that's still in your system at midnight.
• Keep caffeine to before midday for a fortnight, as an experiment. I say this with love and I'm not coming for your coffee. Caffeine stimulates the same stress response you're trying to calm down, so notice what happens to the 3am wake. Some people break caffeine down quickly because of their genetics and some don't, and the slow ones are the most likely to feel an afternoon cup that night.
• Do five minutes of slow breathing, with your out-breath longer than your in-breath, at the time of day your stress usually spikes. It isn't magic, but it's the one technique for switching out of fight-or-flight with consistent evidence behind it, and it's free.

And before you buy anything, ask yourself:

• When did I last have my iron studies and thyroid checked?
• Do I snore, or wake up feeling like I haven't slept?
• Is my 1-3am wake at the same time every night?
• Am I using coffee to get through the afternoon?
• Has anyone actually looked at the whole picture, or just one report?

When to see a doctor promptly

Most of what this article describes is uncomfortable rather than dangerous, and the checks above can wait for a normal appointment. Some things can't.

Palpitations with chest pain, breathlessness, dizziness or fainting need 000, not a stress test. Unexplained weight loss, a sudden severe headache, or bleeding you can't explain need a GP appointment this week. And if low mood has tipped into thoughts of harming yourself, please call Lifeline on 13 11 14, any time.

What to do next

1. Start your two-week notes tonight.
2. Book in with your GP and ask for the bloods by name.
3. Bring up the snoring if it's happening.
4. Then, and only then, decide whether cortisol testing would add anything, and get it read by someone who has seen the rest of the picture.

Not sure whether cortisol testing would tell you anything?

The free call is a conversation, not a consultation. Tell me what your two weeks looked like and what your GP has already checked, and I'll tell you honestly whether testing makes sense yet, even if the answer is "not yet".

Book a free 15-minute call

Fifteen minutes, on the phone, no test required to book it.

Common questions

What are the symptoms of a dysregulated nervous system?

Usually: wired but exhausted, broken sleep with 3am waking, a racing heart over small things, brain fog, digestive upset and irritability. Iron deficiency, thyroid conditions, sleep apnoea, perimenopause and anxiety produce the same list, which is why those are checked first.

Is nervous system dysregulation real?

The pattern is real and common. The label isn't a medical diagnosis and has no agreed definition, so no test can confirm or rule it out. It describes how your stress system is running, with the cause still to be found.

Is there a test for nervous system dysregulation?

No single test. What can be measured is the cortisol rhythm across a day, by saliva or dried urine at home, and heart rate variability against your own baseline. Both show how the stress system is running, not why, and they're most useful after GP bloods and a sleep check.

Can a cortisol test show if my nervous system is dysregulated?

It can show whether your cortisol rhythm is flat, inverted or reasonable, which is useful. It can't show the cause. A flat curve looks the same whether it comes from low iron, poor sleep, perimenopause or ongoing stress.

How do I calm my nervous system?

The measures with the best evidence are unglamorous: the same wake time every day with morning light, protein at breakfast, caffeine only before midday, and five minutes of slow breathing with a longer out-breath. None of them replaces finding out what is driving the pattern.

Does nervous system dysregulation cause weight gain?

Not directly. Ongoing high cortisol, poor sleep and the eating patterns that go with them can all affect weight, and so can an underactive thyroid and perimenopause. If weight has changed without a change in habits, see your GP rather than buying a stress test.

Sources

1. Healthdirect Australia, Stress (the fight-or-flight response, normal versus problematic stress)
2. Healthdirect Australia, Fatigue (causes and when to see a doctor)
3. Healthdirect Australia, Sleep apnoea
4. Stalder T, et al. Assessment of the cortisol awakening response: expert consensus guidelines. Psychoneuroendocrinology, 2016
5. Shaffer F, Ginsberg JP. An overview of heart rate variability metrics and norms. Frontiers in Public Health, 2017
6. Nehlig A. Interindividual differences in caffeine metabolism and factors driving caffeine consumption. Pharmacological Reviews, 2018 (the CYP1A2 fast and slow metaboliser split)
7. UC San Diego Today, Why is everyone "regulating" their nervous system?
8. Healthdirect Australia, Heart palpitations (when to call 000)

Important: This article is general information written by a clinical nutritionist. It isn't medical advice and doesn't replace care from your GP or another qualified health professional. Functional testing doesn't diagnose, treat, cure or prevent any condition, and results are best interpreted alongside your symptoms, history, medications and supplements.

Reviewed by Georgina Waugh

Clinical Nutritionist, BHSc Nutritional Medicine

Last updated: 25 October 2026

Sources reviewed: Healthdirect guidance, the cortisol awakening response consensus guidelines, HRV normative literature, the 2018 review of individual differences in caffeine metabolism, and clinical nutrition interpretation.