FND and POTS: Understanding the Overlap and the Differences

Families navigating FND frequently encounter POTS (Postural Orthostatic Tachycardia Syndrome) in online communities, medical records, and specialist waiting rooms. The two conditions share a frustrating amount of surface territory. Both produce symptoms that fluctuate, both are commonly dismissed or misdiagnosed, both affect more women than men, and both involve the nervous system in ways that standard imaging does not capture. That overlap creates real confusion about what is happening and who should be treating it.

The research is more nuanced than most online summaries suggest. FND and POTS are distinct conditions with different underlying mechanisms, different diagnostic criteria, and different treatment approaches. They can co-occur, but they are not the same thing, and being diagnosed with one does not explain away the other. Understanding where the lines are helps families push for accurate evaluation rather than accepting an incomplete picture.

What POTS Is

Postural Orthostatic Tachycardia Syndrome is a form of dysautonomia, meaning it involves dysfunction of the autonomic nervous system. The autonomic nervous system controls involuntary functions including heart rate, blood pressure, digestion, and temperature regulation. In POTS, standing upright causes an abnormal increase in heart rate, typically defined as an increase of 30 or more beats per minute within 10 minutes of standing, without a corresponding drop in blood pressure sufficient to explain it.

POTS symptoms include lightheadedness, palpitations, brain fog, fatigue, exercise intolerance, nausea, and near-fainting. These symptoms occur primarily or worsen significantly in the upright position and improve when lying down. POTS is diagnosed through tilt table testing or an active stand test with heart rate monitoring, not through symptoms alone.

POTS is not a functional neurological disorder. A 2024 paper by Blitshteyn and colleagues published in Frontiers in Neurology addresses this directly, arguing that POTS and other common autonomic disorders should not be classified as functional neurological disorders. The autonomic dysfunction in POTS has measurable physiological correlates, including abnormal heart rate responses on tilt table testing, reduced plasma volume in some patients, and small fiber neuropathy in a significant subset. These are not features of FND.

Where FND and POTS Genuinely Overlap

The overlap between FND and POTS is real but more limited than community discussions often suggest. A study of 526 participants with FND cited in the Blitshteyn et al. paper found that only 1.9 percent had a POTS diagnosis, making POTS one of the rarest FND comorbidities. The rate of FND among POTS patients across three large studies combining over 5,000 patients was similarly not identified as a common comorbidity in either direction.

What does genuinely overlap is the autonomic nervous system's role in both conditions. A 2024 review in Brain, Behavior and Immunity - Health examined the role of autonomic functioning across FND and comorbid disorders, finding that autonomic dysregulation is measurable across FND, PTSD, anxiety, and depression, and that physical activity may benefit all of these conditions through its effects on autonomic regulation. The autonomic nervous system is involved in FND pathophysiology without FND being an autonomic disorder in the same structural sense as POTS.

The Misdiagnosis Problem in Both Directions

Misdiagnosis runs in both directions between these conditions and the research documents both pathways.

POTS Misdiagnosed as FND

People with POTS who present with movement episodes, tremor, or other visible neurological symptoms can be misdiagnosed with FND if the evaluating clinician does not conduct orthostatic testing. A 2025 case series published in Autonomic Neuroscience described two patients with POTS whose autonomic movement episodes and myoclonic-appearing symptoms were initially diagnosed as FND on hospital admission. Both were correctly diagnosed with POTS after neurologists conducted proper evaluation including orthostatic assessment and tilt table testing. The authors note that POTS-related movement episodes can be visually indistinguishable from functional movement disorder without appropriate testing.

The Blitshteyn et al. paper raises a broader concern about this pattern, noting that patients with post-COVID dysautonomia, post-treatment Lyme disease, and other infection-associated chronic illnesses are frequently misdiagnosed with FND, and that once labeled with FND, patients often have difficulty obtaining further diagnostic and therapeutic care because subsequent complaints are attributed to the functional diagnosis.

FND Misdiagnosed as POTS or Dysautonomia

The reverse also occurs. Patients with FND who have significant autonomic symptoms including palpitations, lightheadedness, and fatigue may be evaluated for POTS and dysautonomia without adequate neurological evaluation for FND. A 2025 narrative review published in Brain Sciences examining comorbidities across FND subtypes found that somatic comorbidities including fatigue syndromes and autonomic symptoms were prevalent across all FND subtypes, reflecting overlapping mechanisms involving interoception and central sensitization. Autonomic symptoms in FND can be genuine features of the condition rather than evidence of a separate autonomic disorder.

What Families Should Ask For

If a family member has received an FND diagnosis and also has significant symptoms that worsen in the upright position, including lightheadedness, palpitations, exercise intolerance, and near-fainting, requesting an autonomic evaluation including orthostatic testing is reasonable. POTS evaluation does not require abandoning the FND diagnosis. Both can be true simultaneously and both can benefit from their own treatment approaches.

If a family member has received a POTS diagnosis and also has significant neurological symptoms that are position-independent, including functional weakness, tremor, gait disturbance, or functional seizures, requesting a neurological evaluation for FND using positive clinical signs is equally reasonable. An autonomic specialist is not the right evaluator for FND. A neurologist or neuropsychiatrist with FND experience is.

Long COVID, POTS, and FND

The post-COVID period has made the POTS and FND overlap more clinically relevant and more publicly discussed. Both conditions increased in documented incidence following COVID-19 infection. Both appear in long COVID presentations. The Blitshteyn et al. paper specifically flags post-COVID dysautonomia patients as being at elevated risk of FND misdiagnosis.

Families dealing with long COVID who are encountering both FND and POTS terminology need to understand that both diagnoses require their own positive evaluation criteria, and that a COVID history does not automatically make either diagnosis more or less appropriate. Both need to be evaluated on their own clinical terms by the right specialists.

For a full overview of FND and what causes it at the neurological level, see our article on what causes FND. For the full FND content library, visit the FND Learning Path.

Educational content only. Robbins Nest Alliance does not provide medical diagnosis or treatment advice. Seek qualified neurological and autonomic specialist care for evaluation of FND and POTS. Content references peer-reviewed research including Frontiers in Neurology, Brain Sciences, Autonomic Neuroscience, Brain Behavior and Immunity - Health, and Neurotherapeutics.