Symptom cluster
Autonomic dysfunction and POTS
Racing heart, dizziness, and feeling worse upright, when standing becomes the hardest part of the day. This page covers: Orthostatic tachycardia (HR rise on standing), Orthostatic intolerance (dizziness, lightheadedness), Fatigue, Exercise intolerance, Exercise intolerance / reduced VO2.
What this is
Your autonomic nervous system runs the things you never have to think about — heart rate, blood pressure, digestion, temperature. In long COVID it can misfire, so the automatic adjustments your body makes when you stand up, eat, or get warm stop happening smoothly.
POTS (postural orthostatic tachycardia syndrome) is the best-known pattern. When you stand, blood pools in your legs and your heart races to compensate — often a rise of 30 or more beats per minute — leaving you dizzy, foggy, and worse the longer you stay upright. The racing heart is the body over-compensating, not a heart that is diseased.
These changes are real and measurable on the right test, such as a stand test or tilt-table — even when a routine ECG or echocardiogram looks completely normal.
How to read this page
Each row under What causes it and What has been tried represents one proposed explanation or treatment. The tags help you judge the claim quickly, without treating every row as equally proven.
gradeHow strong the underlying evidence is.
Example: a treatment tested in multiple randomized controlled trials would receive a stronger grade than one supported only by case reports, expert opinion, or animal studies.
auditHow reliable the claim remains after tracing its sources.
Example: a claim may appear in many reviews, but if those reviews all cite the same small, uncontrolled study, the audit may be weak because the claim is being repeated more than it is being independently confirmed.
A claim can have a strong grade but a weak audit, or the reverse. That is why both are shown.
endpointWhat was actually measured.
Example: a study showing that patients “felt better” measured a patient-reported outcome. A study showing improved oxygen levels, reduced inflammation markers, better walking distance, or abnormal MRI findings measured something different. The endpoint tells you what kind of evidence the claim rests on.
safety / conflictImportant cautions about harm, bias, or financial interests.
Example: a supplement may look low-risk but still interact with medications. A device or drug study may look promising, but if the evidence comes mainly from the manufacturer, that conflict should be visible before the claim is weighed.
What causes it
The leading explanations, each with its evidence grade and audit status.
caused byOrthostatic tachycardia (HR rise on standing)
GPCR autoantibodies (a/b-adrenergic, M2 muscarinic, AT-II receptor) produces Orthostatic tachycardia (HR rise on standing). full page →
Autonomic/small-fiber neuropathy + vagus nerve injury produces Orthostatic tachycardia (HR rise on standing). full page →
Hypovolemia / blood-volume dysregulation produces Orthostatic tachycardia (HR rise on standing).
Platelet storage pool deficiency / low serotonin produces Orthostatic tachycardia (HR rise on standing).
Mast cell activation produces Orthostatic tachycardia (HR rise on standing). full page →
caused byFatigue
Cytokine inflammation driving sympathetic activation produces Fatigue.
caused byExercise intolerance
Physical deconditioning contested-cause Exercise intolerance.
caused byExercise intolerance / reduced VO2
Mitochondrial / metabolic dysfunction produces Exercise intolerance / reduced VO2.
Deconditioning (as cause) contested-cause Exercise intolerance / reduced VO2.
Dysautonomia / autonomic dysfunction produces Exercise intolerance / reduced VO2. full page →
What has been tried
No treatment is approved. Each row shows how strong the evidence is, what it was measured on, and any safety or conflict flag.
tried forOrthostatic intolerance (dizziness, lightheadedness)
Ivabradine relieves Orthostatic intolerance (dizziness, lightheadedness).
Coordinated nonpharmacologic care (bundle) relieves Orthostatic intolerance (dizziness, lightheadedness).
Midodrine relieves Orthostatic intolerance (dizziness, lightheadedness).
Salt + fluid loading relieves Orthostatic intolerance (dizziness, lightheadedness).
Compression garments relieves Orthostatic intolerance (dizziness, lightheadedness).
Pyridostigmine relieves Orthostatic intolerance (dizziness, lightheadedness).
tried forExercise intolerance / reduced VO2
Pyridostigmine improves Exercise intolerance / reduced VO2.
Recumbent / supine-biased rehabilitation (PEM-bounded) manages Exercise intolerance / reduced VO2.
How it is measured
tests forOrthostatic tachycardia (HR rise on standing)
NASA lean / active stand test diagnoses Orthostatic tachycardia (HR rise on standing).
tests forExercise intolerance / reduced VO2
Invasive CPET (iCPET) diagnoses Exercise intolerance / reduced VO2.
Ivabradine lowered heart rate but did not improve symptoms in RECOVER-AUTONOMIC: a surrogate-positive, patient-negative split the page keeps visible.