The picture in most people's head is a gentle slope. Hormones taper off over a few years, symptoms build slowly, and then it is over.
That is not what happens. In the years before your last period the ovary becomes erratic rather than quiet. Estrogen can run higher than it did in your thirties one month and fall away the next. You are not on a slope. You are on a sea.
If you understand this one mechanism, most of what has been confusing you stops being confusing.
Why the ovary becomes erratic
You were born with every egg you will ever have, held in follicles. Each cycle a batch is recruited, one usually wins, and the rest are lost. That pool shrinks across your whole adult life, and in your forties it gets low.
A smaller pool does not simply produce less. It produces unpredictably. The brain, seeing a weaker signal, pushes harder with follicle stimulating hormone. Sometimes the ovary answers loudly and estrogen spikes. Sometimes it barely answers at all. Some cycles no egg is released, and when that happens progesterone, which normally rises in the second half of the cycle, does not.
So the two hormones fall out of step with each other before either of them runs out. That is perimenopause.
What the swing does to you
Read the symptom list again with the mechanism in mind and it stops looking random.
- Sleep. Progesterone has a calming, sleep supporting effect. In cycles where you do not ovulate, it does not arrive. Add night sweats driven by the estrogen drops and you get the three in the morning waking that women describe almost word for word.
- Mood. The brain is full of estrogen receptors, and it responds to change more than to level. Rapid swings, rather than a low value, are what track with irritability, anxiety and tearfulness in this phase. That is why a woman can feel fine for ten days and unrecognizable for four.
- Brain fog. Word finding, concentration and processing speed all take the hit. It is real, it is common, and it is not early dementia, which is the fear almost every woman has and almost none says out loud.
- Heavy or unpredictable bleeding. Estrogen builds the lining. Without regular ovulation, progesterone is not there to organize the shedding. The result is unpredictable, and sometimes very heavy, periods.
- The body. From the later part of this phase, fat mass rises, it moves toward the abdomen and inside it, lean muscle falls, and energy expenditure drops. The 2025 European Society of Endocrinology guideline states this plainly, and notes that the resulting insulin resistance raises the risk of type 2 diabetes.
- Hair and skin. Thinning at the crown and parting, dryness, slower healing. Same underlying shift.
Why your blood test was normal
Because it caught one moment on one morning of one cycle in a system that is oscillating.
A follicle stimulating hormone level that is high in March can be unremarkable in April. An estradiol level can be robust on the day you happened to be bled and low the week you actually felt terrible. This is why the British national guideline is explicit that in women aged 45 and over, perimenopause is diagnosed from the pattern of symptoms, age and menstrual history, and not from routine hormone testing.
A normal result during perimenopause is not evidence that nothing is happening. It is evidence that you were tested on a Tuesday.
Being told your bloods are fine is not the same as being assessed. The pattern is the diagnosis, and reading a pattern properly is a specialist skill, not a checkbox.
What actually needs excluding
This is the other reason a specialist matters. Several conditions imitate this phase closely, and each one has a different answer.
Thyroid disease produces fatigue, weight change, mood change and hair loss. Iron deficiency, which is common in women having heavy perimenopausal periods, produces exhaustion and fog. Sleep apnea produces broken nights and daytime cognitive symptoms and is under diagnosed in women. Depression can be primary rather than hormonal. None of these is rare and none is exotic, and each one is missed regularly when a woman is waved away as being at that age.
What this changes for you
Three things, and they are practical.
First, you can stop treating a normal blood result as proof that you are imagining it. Second, you can stop presenting your symptoms one at a time to different people, because separated they look like six small complaints and together they look like one clear picture. Third, you can stop waiting for it to declare itself, because the years in which this is easiest to influence are the years you are in now.
If you recognize yourself in the swing rather than the slope, that is the conversation worth having. Take it to the specialist and get the pattern read properly, in English or Dutch, by someone whose clinical work is hormones.