Lower Energy and Feeling Unwell? Here's Why

If you're waking up exhausted, aching all over, and feeling like you're fighting off a flu that never quite arrives, you are very likely in the hormonal transition of perimenopause — not imagining things. In my practice, this is one of the most common patterns I see in women over 40: a bone-deep, unrefreshing tiredness layered with a vague, systemic sense of being unwell. Once you understand what's actually happening in your body, there is a great deal you can do about it.

What's happening in your body

Fatigue is, by a wide margin, the symptom I hear about most from women in their 40s and early 50s. Approximately 95% of women report fatigue as a primary symptom during the transition to menopause (source: https://www.myalloy.com/blog/perimenopause-fatigue-symptoms-treatments), and it rarely arrives alone. Oestrogen and progesterone don't decline in a smooth, predictable line — they surge and crash unpredictably for years before your final period, and your body's major systems (brain, adrenal glands, liver, immune system) are all trying to recalibrate in real time. Clinically, once FSH (follicle-stimulating hormone) rises above 25 IU/L, we're looking at a strong indicator that you're firmly in this transition (source: https://www.uclahealth.org/news/article/perimenopause-symptoms-guide), and that hormonal volatility is doing more than affecting your cycle — it's affecting how every cell in your body makes and uses energy.

What I've learned from 20 years of working with women through this transition is that the 'flu-ish, can't-quite-put-my-finger-on-it' feeling so many describe isn't a virus at all — it's what I call the Inflammatory Surge. Oestrogen is a powerful anti-inflammatory buffer in the body. When it drops and fluctuates, that buffer thins, and inflammatory cytokines like IL-6 and TNF-alpha rise. Your brain's hypothalamus — the body's control centre for temperature, hunger, and threat response — reads this cytokine surge as a systemic threat, much like it would an infection. In response, it triggers what's known as sickness behaviour: a biological survival state that forces you to slow down, feel achy, foggy, and low, purely to conserve resources while your internal chemistry sorts itself out. This is a real, measurable physiological event, not a mood or a motivation problem.

Then there's what I refer to with my patients as the Mitochondrial Mismatch. Your mitochondria — the tiny power plants inside every cell — have oestrogen receptors and rely on oestrogen signalling to run efficiently. As that signalling fades and becomes erratic through your 40s, your cells produce less ATP (cellular energy currency) for the same amount of fuel. This is precisely why so many women describe the sensation as 'wading through treacle': it isn't ordinary tiredness that a nap fixes, because the deficit is happening at a cellular level, and sleep alone cannot repair a power-generation problem. Declining oestrogen and reduced mitochondrial efficiency are directly linked, which is why 'just resting more' so often fails to touch this particular kind of exhaustion.

Finally, don't overlook the overnight chemistry. Many women tell me they wake at 3am feeling wired, then crash by mid-morning feeling like they've been hit by a bus. This is what I call the 3am glucose spike: falling progesterone and oestrogen disturb overnight cortisol rhythm, triggering a stress-hormone and blood-glucose release in the small hours that leaves you metabolically 'hungover' by dawn — groggy, foggy, and unwell despite technically having slept. Over 40% of perimenopausal women experience significant sleep disturbances that directly contribute to this persistent exhaustion (source: https://www.get-carrot.com/blog/menopause-and-fatigue-why-energy-drops-during-perimenopause), and the hypothalamic-pituitary-adrenal (HPA) axis sits at the centre of it all — chronically activated, dysregulated, and unable to find its normal rhythm. On top of this, your liver — which is responsible for clearing and metabolising fluctuating hormones — can become genuinely overworked during this transition, and a sluggish liver contributes to that heavy, systemic, almost 'toxic' malaise many women describe but struggle to name.

Is it perimenopause or something else?

Most of the time, this constellation of symptoms is hormonal. But part of good care is ruling out look-alikes, and I always encourage the women I work with to get proper bloodwork rather than assume. Consider these possibilities alongside perimenopause:

• ✦Thyroid dysfunction — thyroid disorders are five to eight times more common in women than men and frequently peak in the 40s and 50s (source: https://www.topdoctors.co.uk/articulos-medicos/7-hidden-causes-of-fatigue-in-women-over-40), and hypothyroidism symptoms overlap almost exactly with perimenopausal fatigue.
• ✦Iron-deficiency anaemia — heavier or more erratic perimenopausal bleeding can quietly deplete iron stores, producing profound tiredness and breathlessness.
• ✦Vitamin B12 or vitamin D deficiency — both are common in midlife and independently cause low energy, low mood, and aching.
• ✦Undiagnosed sleep apnoea — increasingly common around menopause and often missed, especially if you don't snore loudly.
• ✦Chronic Fatigue Syndrome (ME/CFS) or a multi-system illness — this is the one I want you to take seriously. The defining difference is post-exertional malaise (PEM): with hormonal fatigue, a bad day is usually followed by a better one. With ME/CFS, physical or mental exertion triggers a crash that can last days, disproportionate to the effort made.
• ✦Depression or anxiety — mood and energy are deeply intertwined, and treating one without acknowledging the other rarely works.

One diagnostic tool I use with my own patients is what I call pacing as diagnosis, not just treatment. Try a normal, moderate activity — a walk, a work day, a social event — and note what happens in the 24 to 72 hours afterwards. If you feel appropriately tired but recover with rest, that's consistent with perimenopausal fatigue. If it triggers a multi-day crash disproportionate to what you did, that's a signal to push for further investigation beyond 'it's just hormones.'

What you can do about it

• ✦Stabilise blood sugar at every meal, especially breakfast. Pairing protein and fibre with carbohydrates blunts the glucose swings that feed the 3am cortisol spike; insulin sensitivity genuinely declines during this transition, so what worked for you at 30 may not work now.
• ✦Prioritise magnesium glycinate in the evening. In my practice, magnesium depletion is one of the most common and most correctable pieces of this puzzle — it supports both mitochondrial ATP production and a calmer HPA axis, which helps with both the energy deficit and the wired-but-tired feeling.
• ✦Support liver clearance with cruciferous vegetables and adequate B vitamins. A hormone-overwhelmed liver contributes directly to that heavy, systemic malaise; giving it the cofactors it needs to process oestrogen metabolites properly can measurably lift that 'toxic' feeling.
• ✦Address inflammation with omega-3s and a whole-food, lower-sugar diet. Since the flu-like feeling is driven by inflammatory cytokines rather than infection, calming systemic inflammation is one of the most direct ways to reduce sickness behaviour.
• ✦Treat sleep disturbance as a medical issue, not an inconvenience. Night sweats and fragmented sleep are major contributors to daytime exhaustion; cooling strategies, consistent sleep timing, and — where appropriate — hormonal support can make a disproportionate difference.
• ✦Use gentle movement, not intense exercise, while you're in a flare. Overexertion during a cytokine surge often worsens sickness behaviour rather than 'burning it off'; walking, stretching, and breathwork support the nervous system without demanding a mitochondrial output your cells can't currently supply.
• ✦Get a full panel — thyroid, iron, B12, vitamin D, and hormones — before assuming it's 'just perimenopause.' What I see time and again is women dismissed for years before a treatable deficiency or thyroid issue is finally caught.

If you'd like a clearer picture of what's driving your specific pattern of symptoms, a structured self-assessment is a useful starting point before your next appointment.

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Frequently Asked Questions

Why do I feel like I have a permanent low-grade flu during perimenopause? This is the Inflammatory Surge at work. As oestrogen drops, its anti-inflammatory buffering effect weakens, allowing inflammatory cytokines like IL-6 to rise. Your hypothalamus reads this as a threat and triggers 'sickness behaviour' — the same biological response that makes you feel unwell during a real infection, minus the virus.

Is my extreme fatigue just hormones or is it my thyroid? It could genuinely be either, or both. Thyroid disorders are five to eight times more common in women and often emerge in the 40s and 50s (source: https://www.topdoctors.co.uk/articulos-medicos/7-hidden-causes-of-fatigue-in-women-over-40), overlapping heavily with perimenopause symptoms. A simple thyroid panel is essential before assuming hormones are the sole cause.

Why do I wake up feeling unrefreshed even after 8 hours of sleep? Overnight cortisol and glucose disturbances — what I call the 3am glucose spike — mean your body isn't getting genuinely restorative sleep, even if you're technically unconscious for eight hours. Night sweats and fragmented sleep, affecting over 40% of perimenopausal women, compound this (source: https://www.get-carrot.com/blog/menopause-and-fatigue-why-energy-drops-during-perimenopause).

Can perimenopause cause bone-deep exhaustion that rest doesn't fix? Yes. This is the Mitochondrial Mismatch — declining oestrogen signalling reduces your cells' energy production efficiency. Because the deficit is cellular, not simply a lack of hours slept, rest alone often doesn't resolve it; nutrient support and blood sugar stability tend to help more directly.

What is the difference between perimenopause fatigue and Chronic Fatigue Syndrome? The key differentiator is post-exertional malaise. Hormonal fatigue fluctuates but generally recovers with a day's rest. ME/CFS involves a disproportionate, multi-day crash after normal activity. If pacing reveals repeated severe crashes, it's time to investigate beyond perimenopause.

Can hormonal shifts make me feel physically sick or nauseous daily? Yes — fluctuating oestrogen and progesterone affect the gut-brain axis, blood sugar regulation, and inflammatory signalling, all of which can produce genuine nausea, queasiness, or a generalised 'unwell' feeling, separate from any digestive illness.

Related reading

• ✦Why Am I So Tired All the Time in Perimenopause?
• ✦Brain Fog and Memory Lapses in Midlife: What's Normal?
• ✦Perimenopause and Sleep: Why You Wake at 3am

Disclaimer

This content is for educational purposes only and is not a substitute for professional medical advice, diagnosis, or treatment. Always consult a qualified healthcare provider before making decisions about your health.