You’re not imagining it — and neither is the research.

Perigee is a wellness companion, not a medical device. The studies below explain why these signals are meaningful — they are not claims about your body, and nothing here diagnoses or treats anything. One night is a data point; your clinician is the one who interprets.

The calm-signal that dips when you flush

HRV is the tiny beat-to-beat variation in your heart rhythm — a direct readout of the vagus nerve, the body’s brake pedal. Researchers have watched it move in real time with the menopause transition: cardiac vagal control drops during a hot flash or night sweat, most sharply during sleep, and even when a woman never wakes to notice it³.

It isn’t only momentary. As estrogen falls, studies find a lasting shift toward sympathetic (“fight-or-flight”) dominance and lower vagal tone that emerges around the final period⁴, and women with heavier symptoms tend to carry lower overnight HRV overall⁵. So a night that reads below your own range isn’t noise — it’s often your nervous system telling the truth.

A heart that races “over nothing”

Resting heart rate tracks the same autonomic shift from the other side. Even before menopause, wearable studies show resting pulse rises measurably with the hormonal phase — significantly higher in the luteal phase than around menstruation⁷ — and the lasting move toward sympathetic dominance nudges the whole baseline upward⁴.

This is also why it’s worth watching, not ignoring: the American Heart Association calls the menopause transition a window of genuine cardiovascular change and a moment for prevention⁶. A racing heart is rarely an emergency — but it is real, it’s measurable, and it deserves data when you sit down with your clinician.

Night sweats leave a temperature trace

Your overnight wrist temperature moves with your hormones. In wearable studies, nocturnal skin temperature ran about 0.30 °C higher in the luteal phase than the follicular phase⁸, and continuous overnight measurement captures these shifts far more reliably than a single morning reading⁹ — one number is noisy, but a trend isn’t.

There’s a mechanism underneath it. Hot flashes are a thermoregulatory event: the body’s comfortable “do-nothing” temperature band — the thermoneutral zone — narrows dramatically as estrogen falls. In a landmark study, that zone measured about 0.4 °C in women without hot flashes but collapsed to essentially zero in women who had them¹⁰. When the band is that thin, a tiny rise in core temperature trips a flush and a sweat¹¹ — which your wrist then records.

The 3 a.m. wake-up isn’t in your head

Sleep gets measurably harder across this stage. Across large cohorts, the share of women reporting disturbed sleep climbs from roughly 16–42% before the transition to 39–47% during it, and higher still afterward¹². And it’s not just subjective: objective studies using polysomnography and actigraphy show nighttime hot flashes cluster with genuinely fragmented sleep¹².

Perigee reads your night against your own recent baseline — never a population average — so a broken night shows up as what it is: a data point in your pattern, not a verdict.