Reading & sources

The patient-authored guide this whole site tests. Wiggers, living with ME/CFS and POTS, sets out how to read an ordinary Garmin for the signs of a post-exertional crash. It is the primary source for every pattern I tested.

The clinical lineage behind staying under a threshold, the resting-heart-rate ceiling and the two-day exercise test that showed the abnormal recovery in ME/CFS. The 'RHR + 15' kind of rule the guide builds on.

A specialist clinic's guidance on ME/CFS, pacing, and the 'energy envelope', crash prevention written for patients and clinicians, the clinical backdrop to the guide.

A patient-built method, in the same heart-rate-pacing tradition as the guide, for staying under an anaerobic threshold (a resting-heart-rate ceiling, often RHR + 15) to avoid post-exertional crashes. It carries a caveat that matters for this project's own pipeline: Garmin and Polar report resting heart rate as the night's *lowest* HR, which for this patient group may not be true resting heart rate; they recommend using your *average* overnight / sleeping heart rate as the proxy instead.

A standard reference for what heart-rate variability is and what normal looks like, the foundation for reading HRV at all, and for the sleep-stress proxy this site relies on.

Resting heart rate varies widely from person to person and day to day, across 92,000 adults. It is the baseline for judging what an unusual personal-RHR shift even means, and why this site reads signals against your own normal.

Pools 64 case-control studies and finds a reproducible autonomic shift in ME/CFS, higher resting and orthostatic heart rate, a sympathetic tilt, and lower vagal (parasympathetic) HRV. This is the source for the site's line that these bodies tend to sit tilted toward 'activated', with less beat-to-beat variability and slower to settle.

A clear map of what POTS actually is: an excessive heart-rate rise on standing, driven by one (or more) of three mechanisms, low blood volume, over-active sympathetic drive, or partial nerve damage. It is why 'POTS' on this site means a circulation-on-standing problem, and why a single watch signal can't tell the subtypes apart.

Why the site is careful with the word 'POTS.' In POTS the resting autonomic balance tips toward stress, heart-rate variability sits lower, not higher. The watch pattern the guide calls a 'U-dip' is a brief move the other way (a calming blip), so it can't be read as a POTS signal; it's a pattern the participant learned to manage as if it were one.

The honest limit, in one paper: in ME/CFS and long COVID, blood flow to the brain can fall on standing even when heart rate and blood pressure look completely normal. A wrist watch reads heart rate, so it is blind to this whole class of orthostatic trouble, the reason this site never claims the watch 'sees your POTS.'

An independent, pre-registered, peer-reviewed study validating Garmin's stress score against gold-standard ECG heart-rate-variability. The evidence that the sleep-stress HRV proxy used here stands on something real.

The white paper for the algorithm Garmin uses, how a 0–100 stress score is computed from beat-to-beat heart-rate-variability. The reason stress and HRV are two views of one underlying signal.

A flagship synthesis of what is known about Long COVID's biology and the search for treatments, the big-picture context for why a body might behave the way this one does.

A landmark synthesis of long COVID. It anchors the site's framing that post-exertional malaise is reported by a majority of patients, and that dysautonomia and POTS are commonly found, while noting that large-population, diagnosis-specific prevalence figures are still sparse.

The source for the site's line that standing intolerance is common while a confirmed POTS diagnosis is a smaller subset: this review reports that roughly 2–14% of COVID survivors develop POTS and 9–61% experience POTS-like symptoms in the months after infection, the figures swinging widely with who is studied and whether POTS is confirmed by a standing or tilt-table test.

Muscle biopsies before and after exertion in long COVID patients show real, physical damage after a crash, among the strongest evidence that post-exertional malaise is not simply deconditioning.

Pulls together the studies on how Long COVID affects heart-rate variability, the autonomic-dysregulation picture in one place, instead of reading each cohort.

The best current synthesis of whether antidepressants move the autonomic nervous system. Across 30 studies it found SSRIs have no or inconclusive effects on most heart-rate-variability measures, and the one measure that did move pointed in opposite directions depending on study design. The anchor for this site's 'the HRV story is mixed' line, and for the distinction that the strongly HRV-lowering drugs are the older tricyclics, not SSRIs.

The strongest single signal that SSRIs can lower HRV, and it names citalopram. In over 10,000 adults, users of every SSRI except fluoxetine had lower heart-rate variability than non-users, with citalopram's effect milder than paroxetine's. Cross-sectional, so it can't prove cause, but it's the closest the literature comes to a citalopram-specific result.

The paper that energised the 'give an SSRI for long COVID' idea: it proposed that post-viral inflammation depletes serotonin and thereby dampens vagus-nerve signalling and memory. Influential and ambitious, and, as the commentary filed next to it argues, methodologically contested. Read the two together.

The strongest randomised evidence for an SSRI in COVID. Fluvoxamine, started early in acute infection, cut hospitalisation, probably through an anti-inflammatory (sigma-1) action rather than its serotonin effect. Crucially this is about the acute illness, not treating established long COVID.

Carla Rus's study, the work that put this intervention on my radar. 95 post-COVID patients treated with SSRIs, most of whom improved, brain fog and sensory overload most of all. Exploratory by its own description: a questionnaire study with no control group, so it raises the hypothesis rather than settling it.

Evidence that emotional blunting is a real, recognised SSRI effect, reported more often with serotonergic antidepressants than others, citalopram among them, and one of the side effects most tied to dissatisfaction. The backdrop to my own experience of feeling toned-down.

Why an athlete's resting heart rate runs low, endurance training shifts autonomic balance toward the parasympathetic and lowers resting heart rate (training bradycardia), and the effect fades when training stops. The mechanism behind this record's fitness driver: a trained-low resting heart rate that drifts back up as activity falls away, and that masked the infection's heart-rate rise in the COVID check.

External evidence that a consumer wristband's resting-heart-rate signal really does move for an infection, here, shifts around COVID-19 that were often detectable before symptoms. The population-scale backdrop to this site's single-person COVID check: the watch moving for a known infection is an established phenomenon, not a one-off.

The reporting standard for single-person (n-of-1) trials, the discipline for doing a study of one body credibly. The pre-registration practice on this site follows it.