Doctor Explains: Orthostatic Intolerance — Why Do I Feel Dizzy When Standing? Managing POTS and Heart Rate Fluctuations in ME/CFS
- Dr Dmitry Pshezhetskiy
- 5 days ago
- 5 min read
Have you ever stood up and suddenly felt dizzy, light-headed, shaky, weak, or as though your heart is racing?
For people living with ME/CFS (Myalgic Encephalomyelitis/Chronic Fatigue Syndrome), this can be surprisingly common. Some people find that simply standing in a queue, taking a shower, cooking a meal, or having a conversation while upright can leave them feeling unwell.
This is often related to something called orthostatic intolerance — difficulty tolerating being upright.
As an ME/CFS specialist, I frequently see patients experiencing dizziness, palpitations and heart-rate fluctuations alongside fatigue, brain fog and Post-Exertional Malaise (PEM).
In this article, I will explain why this happens, how conditions such as Postural Orthostatic Tachycardia Syndrome (POTS) may be involved, and what can be done to manage these symptoms.
What Is Orthostatic Intolerance?
Orthostatic intolerance simply means that symptoms become worse when you are upright — particularly when standing — and improve when you sit or lie down.
Symptoms can include:
Dizziness or light-headedness
Racing or pounding heartbeat
Palpitations
Feeling faint
Weakness or shakiness
Blurred or altered vision
Brain fog
Nausea
Headache
Sweating
Breathlessness
Chest discomfort
Extreme fatigue
Some people may actually faint, although many never do.
The important point is that these symptoms are not necessarily caused by anxiety or simply being unfit. They can result from problems regulating heart rate, blood pressure and blood flow when the body changes position.
Why Does Standing Affect People With ME/CFS?
When a healthy person stands, gravity causes blood to move towards the legs and abdomen.
The body normally compensates automatically. Blood vessels tighten, the heart adjusts its rate, and the nervous system works rapidly to maintain enough blood reaching the brain.
In some people with ME/CFS, this automatic regulation does not work as efficiently.
The autonomic nervous system — the part of the nervous system controlling automatic functions such as heart rate, blood pressure, digestion and temperature regulation — may behave differently.
This is sometimes described as dysautonomia.
It helps explain why somebody may feel relatively comfortable lying down but considerably worse after standing for several minutes.
POTS, ME/CFS and Post-Exertional Malaise (PEM)
One form of orthostatic intolerance is Postural Orthostatic Tachycardia Syndrome (POTS).
POTS involves an excessive increase in heart rate after becoming upright, together with symptoms of orthostatic intolerance, without the blood-pressure drop required to explain the tachycardia.
POTS and ME/CFS are different conditions, but they can overlap.
For example, someone might notice their resting heart rate is around 65–75 beats per minute while lying down, but it rises considerably after standing.
They may then experience dizziness, palpitations, brain fog and exhaustion.
However, heart rate alone cannot diagnose POTS. Proper assessment is important because dehydration, anaemia, thyroid problems, medications, heart rhythm abnormalities and other medical conditions can produce similar symptoms.
How Can Orthostatic Intolerance Trigger Post-Exertional Malaise (PEM)?
One important and sometimes overlooked issue is that standing itself requires energy.
Someone with ME/CFS does not necessarily have to exercise to exceed their limits.
Standing while cooking for 20 minutes, showering, travelling on public transport or waiting at a checkout can represent significant physiological stress.
For somebody susceptible to Post-Exertional Malaise (PEM), this may contribute to a delayed worsening of symptoms later that day or even the following day.
The person may subsequently experience increased fatigue, pain, brain fog, flu-like feelings, sleep disturbance and worsening dizziness.
Recognising this connection is an important part of ME/CFS therapy and symptom management.
Post-Exertional Malaise (PEM): Why "Pushing Through" Can Backfire
People are sometimes advised to improve their tolerance by simply standing for longer or exercising more.
For someone with ME/CFS and Post-Exertional Malaise (PEM), this approach needs considerable caution.
Repeatedly pushing beyond the person's energy limits can worsen symptoms rather than improve them.
Instead, management needs to take account of the individual's energy envelope and their susceptibility to PEM.
For example, sitting down while preparing food, using a shower seat, avoiding unnecessarily long periods standing still and breaking activities into shorter stages can reduce the body's overall workload.
These adaptations aren't "giving in" to the illness.
They are ways of using limited energy more efficiently.
What About Long COVID, POTS and Post-Exertional Malaise (PEM)?
Orthostatic intolerance isn't limited to ME/CFS.
Similar symptoms are increasingly recognised in people with Long COVID, particularly those experiencing persistent fatigue, palpitations, brain fog and Post-Exertional Malaise (PEM).
Patients attending a Long COVID fatigue clinic may therefore require assessment not only of fatigue but also of cardiovascular and autonomic symptoms.
Likewise, people seeking a post viral fatigue doctor following another infection may describe similar symptoms.
Understanding whether orthostatic intolerance is contributing can sometimes explain why apparently simple activities — such as showering or standing during a conversation — feel disproportionately exhausting.
How Is Orthostatic Intolerance and POTS Investigated?
Assessment begins with listening carefully to the symptoms and their pattern.
Questions might include:
What happens when you stand?
How quickly do symptoms appear?
Does lying down make them better?
What happens to your heart rate?
Have you ever fainted?
Are symptoms worse after meals, heat or showers?
Does standing contribute to Post-Exertional Malaise (PEM)?
Heart rate and blood pressure can then be assessed while lying down and after standing.
Depending on the circumstances, further assessment or referral may be appropriate.
Importantly, ME/CFS testing is not about assuming every symptom must be caused by ME/CFS. Good medical assessment means considering other explanations and excluding conditions requiring different treatment.
Managing Orthostatic Intolerance Without Worsening Post-Exertional Malaise (PEM)
Management should be individualised, particularly where ME/CFS is present.
Depending upon someone's medical circumstances, strategies can include:
Maintaining appropriate hydration
Avoiding prolonged standing
Changing position gradually
Sitting rather than standing for everyday activities
Avoiding excessive heat where this triggers symptoms
Smaller meals if large meals worsen symptoms
Compression garments in selected patients
Monitoring symptoms alongside heart rate
Pacing activity to reduce Post-Exertional Malaise (PEM)
Some patients may benefit from medication when non-drug measures are insufficient, but this requires individual medical assessment because treatment depends upon the underlying problem, blood pressure, other conditions and medications.
Fibromyalgia, Orthostatic Symptoms and Post-Exertional Malaise (PEM)
There can also be overlap between fibromyalgia, ME/CFS and symptoms of autonomic dysfunction.
People searching for a fibromyalgia specialist online may initially focus on widespread pain, but also experience fatigue, disturbed sleep, brain fog, dizziness and palpitations.
This overlap is why looking at the whole clinical picture is important rather than treating every symptom separately.
What Does Current ME/CFS Research Tell Us?
Autonomic dysfunction and abnormalities of cardiovascular regulation continue to be important areas of ME/CFS research.
Research is investigating how the autonomic nervous system, circulation, immune system and energy metabolism may interact in ME/CFS and related post-viral conditions.
There are still many unanswered questions.
This means we should be careful about treatments advertised as correcting the "root cause" of POTS or ME/CFS without good evidence.
Effective ME/CFS therapy should instead combine evidence-based medicine with careful symptom management and realistic pacing.
When Should You Speak to an ME/CFS Specialist?
If you repeatedly experience dizziness, racing heart, weakness, brain fog or feeling faint when standing — particularly alongside persistent fatigue and Post-Exertional Malaise (PEM) — it is worth discussing these symptoms with a healthcare professional.
An ME/CFS specialist or online ME/CFS doctor can review the overall pattern, consider possible alternative diagnoses, discuss appropriate investigations and determine whether orthostatic intolerance may be contributing to your symptoms.
New or severe chest pain, fainting, significant breathlessness or a new persistent rapid/irregular heartbeat should not simply be assumed to be ME/CFS or POTS and may require urgent medical assessment.
If you found this article helpful, you can also browse our complete collection of educational articles on ME/CFS research, ME/CFS testing, ME/CFS therapy, Long COVID and post-viral illness on our blog:
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About the doctor: About Prof. Dmitry Pshezhetskiy
ME/CFS and related conditions: Articles and resources
Prof. Dmitry Pshezhetskiy, MBBS, PhD, MRCGPGMC 7494518 — Registered Medical Practitioner (GP)admin@ukmecfsspecialist.co.uk
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