FND and POTS: How They're Linked and How to Tell Them Apart

What Is Functional Neurological Disorder?

Functional neurological disorder (FND) describes genuinely experienced problems with movement, sensation or thinking that come from how the nervous system is working. The most common forms are functional seizures, also called dissociative or psychogenic non-epileptic seizures, and functional movement disorders such as tremor, jerks, weakness and trouble walking (Hallett, 2022). The symptoms run through the parts of the nervous system you normally control on purpose, yet they happen involuntarily.

FND is also common. In a study of 3,781 new patients at neurology clinics across Scotland, functional and psychological symptoms were the second most common diagnosis group at 16%, after headache at 19% (Stone, 2010).

Is FND Real or Psychological?

FND has carried older labels, including conversion disorder and psychogenic disorder (Hallett, 2022), and those labels came with an assumption of faking. When UK neurologists were surveyed, most saw feigning as entangled with conversion disorder (Kanaan, 2011). A later survey of psychiatrists found they saw feigning as usually present to a degree (Dent, 2020).

Researchers who study FND now describe the symptoms as genuinely experienced, and they point out that there's no more reason to suspect faking in FND than in pain or fatigue (Hallett, 2022). Our team agrees, and adds a practical point: when symptoms change with your position, the nervous system is showing you something that can be measured.

FND vs POTS: What's the Difference?

FND is defined by the pattern of symptoms on a neurological exam. POTS is defined by what your heart rate does when you stand. One person can meet both definitions, and a diagnosis of one doesn't rule out the other.

	FND	POTS
What it is	Real, involuntary movement, sensory or thinking symptoms from how the nervous system is working	A heart rate rise on standing that compensates for poor blood flow to the brain
How it's diagnosed	Positive signs on a neurological exam, and video EEG for functional seizures	A rise of 30 or more beats per minute within 10 minutes of standing (40 or more ages 12 to 19), with no drop in blood pressure
Common symptoms	Functional seizures, tremor, jerks, weakness, trouble walking, numbness	Lightheadedness, palpitations, shakiness, weakness, blurred vision and fatigue when upright
Does standing matter?	It isn't part of the definition, though upright stress can make symptoms worse	Standing is the trigger, and symptoms ease when you lie down

POTS is one form of dysautonomia, the umbrella term for problems with the autonomic nervous system, which runs heart rate, blood pressure, digestion and temperature. FND involves the systems that handle movement and sensation. They're different systems, and a person can have trouble in both (Vernino, 2021; Hallett, 2022).

Can You Have FND and POTS Together?

Yes, you can. A 2026 case report described an 18-year-old woman with FND whose leg weakness, falls and need to lie down had all been put down to the functional diagnosis. A tilt test showed POTS. With care for both, she went from using a wheelchair to standing on her own over several months (Das, 2026). The authors' conclusion applies widely: a functional diagnosis shouldn't stop anyone from checking for an autonomic problem.

The mix-up runs the other way too. In a Boston series of 17 adults whose seizure-like spells had first been labeled functional, every patient showed features of orthostatic hypotension. Most were older, with a median age of 64. Fourteen started medication aimed at the autonomic problem, and 10 reported improvement, including fewer or no abnormal movements (Khoo, 2026).

FND researchers also say treating co-existing orthostatic intolerance matters (Hallett, 2022). Our team's view is that brain blood flow is the link. In people with POTS, blood flow speed in the brain's main arteries fell about twice as much as in healthy controls during a tilt test, 19.5% versus 10.3% (Ocon, 2009). When standing pulls blood away from the head, the pathways that produce FND symptoms have less to work with and misfire more. That's why being upright can make FND symptoms worse and lying down can help.

Can FND Cause Fainting, Palpitations or Blood Pressure Changes?

FND can produce episodes that look like fainting, and a tilt test can tell them apart from true fainting. In 43 functional fainting episodes recorded on the tilt table, heart rate and blood pressure rose before and during the apparent faint, the EEG didn't change, and the eyes were closed in 97% of them. In vasovagal fainting, blood pressure falls and the eyes usually stay open (Tannemaat, 2013).

The 2 can also happen in the same person. Across 1,164 tilt tests at 2 syncope centers, true fainting and functional fainting showed up together more often than chance would predict (Blad, 2015).

Palpitations and blood pressure swings aren't part of how FND is defined (Hallett, 2022). Children and teens with functional symptoms do run a faster resting heart rate than healthy peers, 82 versus 74 beats per minute on average, with less heart rate variability (Kozlowska, 2015). When palpitations or lightheadedness come with standing, though, they point to the autonomic system. Our team measures heart rate, blood pressure and brain blood flow together on a tilt table, because that combination shows which system is driving an episode.

Case Study: FND, Fainting and Functional Seizures at 17

This case comes from our clinic. It shows how our team works through FND when standing makes it worse. It's one person's story, so it can't serve as a treatment plan for everyone with FND, and none of it is meant to be tried at home.

What she came in with

A 17-year-old had a history of fainting and had been diagnosed with FND. Her episodes went beyond dropping to the floor. They came with jerking of her limbs and head, a tremor, legs that gave out, and a drift to one side when she walked that she couldn't control, and she was using a wheelchair. The episodes happened several times a day and kept increasing. During a hospital EEG with flashing lights, they became more frequent, longer and more physical.

Each episode usually lasted a couple of minutes and sometimes up to an hour. During one she couldn't speak or move, though she could still hear what was going on around her. Too much mental or physical activity made them worse, and so did simply being upright. Lying down was the only thing that helped. IV saline in the hospital gave her several hours of relief, and a physician there noticed that her racing heart and palpitations came mostly when she stood.

What we found

Our testing confirmed it. When she was upright, her blood pressure dipped. It stayed short of orthostatic hypotension, but the dip was enough that her heart rate climbed to make up for it. Transcranial Doppler of the middle cerebral artery showed less blood reaching her brain. On the tilt table her symptoms came on one side at a time: repetitive movements in her right leg, posturing of her head to one side and fluttering of her eyes in one direction. That one-sided pattern pointed to specific pathways losing blood flow rather than the whole brain at once.

Her eye movements told the same story. Testing was done seated, so she was already partly upright. When she jumped her eyes between targets up and down, the movements were slow and delayed, with a small swirl where they should have snapped, and her eyes drifted left as her head turned right. When she smoothly tracked a target up and down, her eyes jerked side to side. A Maddox rod test showed her 2 eyes aiming at slightly different points 20 feet away. Our team reads those findings as a problem in how the cerebellum, brainstem and frontal lobe work together, the network that coordinates eye movement, posture and blood delivery to the brain.

What we did

We found the position where things started to fail and began below it, lying flat. While she fixed her gaze on a target, a clinician turned her head about 3 degrees each way and guided the rotation of her spine. She didn't generate the movement herself, so her body only received feedback about it.

That mattered because FND involves a mismatch between movement that feels voluntary and what the motor and sensory systems actually do. Moving her passively supplied clean sensory input without asking her to produce the movement. Her movements smoothed out, and we raised her toward upright in small steps, watching for the leg movements, the sharpness of her eye movements and any convergence spasm.

Outcome and timeline

Within days she could sit up, move and walk without drifting to the side, with longer gaps between episodes, and she handled eye movement and busy surroundings better each session. A repeat of the vertical tracking test a couple of days in still wasn't perfectly smooth, but the side-to-side jerks and the swirl were gone. Once she was upright and could turn her own head, she moved to our whole-body rotation chair, which calmed the jerking movements further. After a couple of weeks, the work moved to tools she could use at home, and she got out of the wheelchair and back to school. One patient's result can't predict anyone else's, and FND varies widely from person to person.

How Is FND Treated?

Standard FND care is tailored, multidisciplinary treatment that can include physical and psychological therapy (Hallett, 2022). FND-specific physiotherapy has some of the best evidence, and it still has a ceiling. In the largest trial so far, with 355 adults with functional motor symptoms, it didn't beat standard neurological physiotherapy on physical function at 12 months, though more of the people who had it rated themselves improved (Nielsen, 2025). Treating what comes along with FND matters too, including migraine, orthostatic intolerance, anxiety and depression (Hallett, 2022), and medication can help with several of those.

Our team adds one question to that workup: do the symptoms change when you stand? If they do, we measure heart rate, blood pressure and brain blood flow on a tilt table with transcranial Doppler, find the position where symptoms start, and build rehabilitation up from below that point, as in the case above.

FND and POTS: FAQ

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