If you have been told you may have fibromyalgia, or you are living with widespread pain, fatigue, brain fog, poor sleep or symptoms that have not been fully explained, it can be difficult to know what is causing what.
I often see patients who have been given a label such as fibromyalgia, ME/CFS, long Covid, functional neurological disorder or medically unexplained symptoms, but still feel something has been missed.
Fibromyalgia is real. The symptoms can be distressing and life-limiting. But it is also important to remember that symptoms such as tiredness, pain, pins and needles, dizziness, low mood and brain fog can overlap with B12 deficiency, iron deficiency, anaemia, thyroid disease, vitamin D deficiency and other medical problems.
My aim in this guide is to explain fibromyalgia symptoms clearly, help you understand where there can be overlap and show when it may be sensible to review the wider clinical picture.
What is fibromyalgia?
Fibromyalgia, sometimes called fibromyalgia syndrome, is a long-term condition that causes pain all over the body. It is also commonly linked with fatigue, poor sleep, increased sensitivity to pain, brain fog, headaches, irritable bowel syndrome and mood symptoms.
The exact cause is not fully understood. The NHS explains that fibromyalgia may involve changes in how the central nervous system – the brain, spinal cord and nerves – processes pain messages.
That does not mean the symptoms are imaginary. It means the body’s pain and sensory systems may become more sensitive and reactive.
There is no single blood test, scan or X-ray that confirms fibromyalgia. Diagnosis is usually based on symptoms, history, examination and ruling out other conditions that may cause similar symptoms.
The main symptoms of fibromyalgia
Fibromyalgia can look different from person to person. Some people mainly experience widespread pain. Others are more affected by fatigue, sleep disturbance, brain fog, dizziness or symptoms that flare and settle over time.
1. Widespread pain
The main symptom of fibromyalgia is widespread pain. This may feel like aching, burning, stabbing, throbbing or deep muscle pain. It may affect both sides of the body and can move from one area to another.
Some people describe feeling as though they have flu-like body aches, even when they are not unwell with an infection.
2. Increased sensitivity to pain
Fibromyalgia can make the body more sensitive to pain. Things that would usually feel mildly uncomfortable may feel much more painful than expected. The NHS describes increased sensitivity to pain as one of the symptoms of fibromyalgia.
This can make everyday activities difficult, especially when pain feels unpredictable.
3. Muscle stiffness
Many people with fibromyalgia experience stiffness. This may be worse in the morning, after sitting still or after doing more activity than usual.
Stiffness can make it harder to get moving, exercise, work or complete normal daily tasks.
4. Fatigue and exhaustion
Fatigue in fibromyalgia can be more than ordinary tiredness. It may feel like heavy, whole-body exhaustion that does not fully improve with rest.
The NHS lists tiredness linked to poor sleep as a common symptom of fibromyalgia, and fatigue is one of the symptoms that often affects quality of life.
This is also where overlap matters. Fatigue can also be caused by B12 deficiency, iron deficiency anaemia, thyroid disease, vitamin D deficiency, sleep problems, low mood and other medical conditions.
5. Poor sleep or waking unrefreshed
Many people with fibromyalgia struggle to get to sleep, stay asleep or wake feeling unrefreshed. Poor sleep can then make pain, mood, concentration and fatigue worse.
A careful review should consider sleep quality, pain, medication, stress, restless legs, low iron, thyroid symptoms and other factors that may be contributing.
6. Brain fog
“Fibro fog” is a common way of describing problems with memory, concentration, word-finding or mental clarity. The NHS describes problems with mental processes in fibromyalgia, such as difficulty concentrating or remembering things.
Brain fog can also occur in B12 deficiency, thyroid disease, sleep disruption, low mood, long Covid, ME/CFS and other conditions. NICE information for the public also recognises memory and concentration problems as possible features of B12 deficiency.
7. Headaches and migraine-type symptoms
Headaches can occur alongside fibromyalgia. Some people also describe migraine-type symptoms, pressure, facial pain or sensitivity to light and sound. The NHS lists headaches among symptoms that may occur with fibromyalgia.
If headaches are new, severe, sudden, worsening or associated with neurological symptoms, they should be assessed urgently.
8. Digestive symptoms
Irritable bowel syndrome, often called IBS, can occur alongside fibromyalgia. This may include abdominal pain, bloating, diarrhoea, constipation or alternating bowel habit. The NHS lists IBS as one of the symptoms associated with fibromyalgia.
Digestive symptoms can also be relevant when thinking about nutrient absorption, including B12, iron, folate and vitamin D.
Symptoms that can overlap with fibromyalgia
One of the challenges with fibromyalgia is that the symptoms are not unique to one condition. This is why a careful assessment matters.
1. B12 deficiency
B12 deficiency can cause symptoms such as extreme tiredness, pins and needles, mouth ulcers, muscle weakness, memory problems and changes in mood or thinking.
This does not mean B12 deficiency is always the cause of fibromyalgia-type symptoms. It means B12 should be considered when the symptom pattern fits, especially if there are risk factors such as pernicious anaemia, gut absorption problems, vegan diet, medication effects or nitrous oxide exposure.
2. Iron deficiency and anaemia
Iron deficiency anaemia can cause tiredness, shortness of breath and palpitations. Some people also experience weakness, dizziness, reduced exercise tolerance, restless legs or feeling generally drained.
Low ferritin or recurrent iron deficiency may be especially relevant if symptoms include heavy periods, breathlessness on exertion, restless legs or poor exercise tolerance.
3. Thyroid disease
An underactive thyroid can cause tiredness, weight gain, low mood, muscle aches and weakness. These can overlap with symptoms often described in fibromyalgia.
A thyroid blood test may be useful where symptoms, history or previous results suggest it.
4. Vitamin D deficiency
Vitamin D can be relevant in a wider picture of fatigue, aches, weakness and poor wellbeing. It is not the explanation for every pain syndrome, but it may be one piece of the clinical jigsaw.
5. ME/CFS and long Covid
ME/CFS and long Covid can overlap with fibromyalgia, especially where fatigue, brain fog, pain, poor sleep, dizziness or post-exertional worsening are present. NICE guidance on ME/CFS recognises debilitating fatigue, post-exertional malaise, unrefreshing sleep and cognitive difficulties as core features of ME/CFS.
If symptoms worsen significantly after activity and recovery is prolonged, that pattern should be discussed carefully with a clinician.
6. Inflammatory or autoimmune conditions
Some inflammatory, autoimmune or rheumatological conditions can cause pain, fatigue, stiffness and systemic symptoms. Fibromyalgia can also exist alongside other diagnoses, so the aim is not to force everything into one label.
What fibromyalgia pain can feel like
Patients describe fibromyalgia pain in many different ways. There is no single “correct” description.
It may feel like:
- A deep ache – often described as muscle or whole-body soreness.
- Burning or stinging pain – sometimes difficult to localise.
- Sharp or stabbing pain – which may come and go.
- Tenderness to touch – where pressure, clothing or light contact feels uncomfortable.
- Flu-like body pain – as if the body is fighting an infection.
- Pain that moves around – affecting different areas on different days.
Pain that is severe, sudden, associated with swelling, redness, fever, chest pain, weakness on one side, new bladder or bowel problems or unexplained weight loss should not be assumed to be fibromyalgia.
Why fibromyalgia symptoms can flare
Fibromyalgia symptoms can change. The NHS notes that symptoms can sometimes improve or get worse suddenly.
Common flare patterns patients describe include:
1. After physical overexertion
Doing too much activity, lifting, travelling or standing for long periods can sometimes trigger a flare.
2. After poor sleep
Sleep disruption can make pain, fatigue, mood and concentration worse.
3. During stress or emotional strain
Stress does not mean symptoms are “just psychological”. The nervous system, hormones, sleep and pain processing are closely linked.
4. Around infection or illness
Some people notice symptoms worsen after viral infections or other physical stressors. The NHS notes that fibromyalgia may be triggered by physical or emotional stress, including infection, injury or stress.
5. With hormonal or menstrual changes
Some patients notice pain, fatigue or dizziness change around their cycle, especially where heavy periods or low iron are also present.
6. When another deficiency or condition is present
If B12 deficiency, iron deficiency, thyroid disease, inflammation or another condition is also present, symptoms may feel more intense or harder to interpret.
How fibromyalgia is diagnosed
Fibromyalgia can be difficult to diagnose because symptoms vary and can be similar to several other conditions. The NHS explains that there is no specific test for fibromyalgia, and that urine tests, blood tests, X-rays or scans may be used to check for other conditions.
A sensible assessment may include:
1. A careful symptom history
This means looking at pain, fatigue, sleep, brain fog, mood, dizziness, digestive symptoms, nerve symptoms and how long the pattern has been present.
2. A review of medical history
Previous diagnoses, infections, injuries, surgery, autoimmune conditions, medications and family history can all be relevant.
3. Examination where appropriate
A clinician may assess joints, muscles, nerves, balance, strength, reflexes or other areas depending on symptoms.
4. Blood tests to look for other causes
Blood tests may be used to check for conditions that can cause similar symptoms, such as anaemia, thyroid disease, inflammatory conditions or deficiency states.
5. Review of symptom pattern over time
Fibromyalgia symptoms often fluctuate. A symptom diary can help show patterns, triggers, response to treatment and whether something else needs attention.
6. Referral where needed
If there are red flags, diagnostic uncertainty, abnormal tests or features suggesting another condition, referral to the right specialist may be needed.
When to consider a wider metabolic assessment
If you have been diagnosed with fibromyalgia, it does not mean every future symptom should automatically be attributed to fibromyalgia.
A wider review may be useful if:
1. Your symptoms have changed
New, worsening or different symptoms deserve proper assessment.
2. You have neurological symptoms
Pins and needles, numbness, burning feet, balance problems, weakness or memory changes can overlap with fibromyalgia, but they can also occur in B12 deficiency or other neurological conditions.
3. You have low or borderline blood results
Low ferritin, low B12, low folate, low vitamin D, thyroid abnormalities or anaemia should be interpreted in context.
4. You have symptoms despite treatment
If pain treatment, pacing, exercise changes, B12 injections, iron treatment or supplements have not helped as expected, the plan should be reviewed.
5. You have risk factors for deficiency
These may include vegan or restricted diet, gut symptoms, autoimmune gastritis, pernicious anaemia, heavy periods, medication effects, bariatric surgery or nitrous oxide exposure.
6. You feel the diagnosis has closed the door
A fibromyalgia diagnosis should not prevent careful medical thinking. It should help guide care while still allowing other treatable issues to be recognised.
What I look at at B12 Metabolic Clinic
At B12 Metabolic Clinic in Reading, I do not diagnose fibromyalgia online and I do not claim that B12 or iron explains every symptom.
My role is different. I look for treatable deficiency-related or metabolic contributors that may overlap with fibromyalgia-type symptoms.
I may review:
- B12 and folate – especially with brain fog, pins and needles, memory issues, mouth symptoms, balance changes or risk factors for poor absorption.
- Ferritin and iron studies – especially with low stamina, breathlessness, palpitations, restless legs, heavy periods or recurrent low iron.
- Full blood count – to check for anaemia patterns and wider blood markers.
- Vitamin D and thyroid function – where fatigue, weakness, aches, low mood or poor recovery are part of the picture.
- Inflammation and autoimmune context – particularly if symptoms suggest inflammatory disease, autoimmune gastritis or another systemic issue.
- Medication, diet and gut absorption – because these can affect B12, iron, folate, vitamin D and the wider clinical picture.
If B12 deficiency, iron deficiency, anaemia or another treatable issue looks relevant, I will explain why. If it does not, I will say so clearly.
Managing fibromyalgia symptoms
Fibromyalgia management is usually about reducing symptom burden and improving quality of life rather than expecting one single cure. The NHS explains that treatment can ease symptoms, although they are unlikely to disappear completely, and that treatment may include exercise programmes, relaxation techniques, talking therapies and medicines such as antidepressants.
Helpful approaches may include:
1. Understanding your symptom pattern
Knowing what flares symptoms, what helps recovery and what signals something new can make the condition feel less unpredictable.
2. Pacing activity
Pacing means balancing activity and rest so you avoid repeated cycles of overdoing things and then crashing.
3. Gentle movement
Exercise can help some people with fibromyalgia, but it needs to be introduced carefully and at a level that is realistic for the person. The NHS notes that exercise can have important benefits for people with fibromyalgia, including helping to reduce pain.
4. Improving sleep where possible
Sleep is not always easy to fix, but reviewing pain, restless legs, routine, mood, medication, caffeine, alcohol and iron status may help identify practical steps.
5. Reviewing medication and pain support
Some people benefit from medication or pain management support. This should be discussed with your GP or relevant clinician, especially if symptoms are severe or affecting daily life.
6. Looking for treatable contributors
Treating iron deficiency, B12 deficiency, thyroid disease or another medical issue will not necessarily “cure” fibromyalgia, but it may reduce overlapping symptoms if those issues are present.
When symptoms need urgent medical help
Fibromyalgia can cause long-term pain and fatigue, but some symptoms should not be assumed to be part of fibromyalgia.
Please seek urgent help through NHS 111, 999 or A&E if you have:
- Severe chest pain or sudden shortness of breath
- Fainting, collapse or severe palpitations
- Weakness on one side of the body or new speech problems
- New confusion, severe headache or sudden neurological symptoms
- Black stools, vomiting blood or heavy bleeding
- Rapidly worsening weakness, problems walking or symptoms that feel unsafe to wait
If you are unsure whether symptoms are urgent, it is safer to seek medical advice.
FAQs
- Can fibromyalgia cause tiredness?
Yes. Fatigue is a common symptom of fibromyalgia and may be linked with poor sleep, pain and nervous system sensitivity. Tiredness can also be caused by B12 deficiency, iron deficiency anaemia, thyroid disease, low mood, sleep problems and other medical conditions, so context matters.
- What does fibromyalgia pain feel like?
Fibromyalgia pain is often widespread and may feel aching, burning, stabbing, tender or flu-like. It can move around the body and vary from day to day. The main symptom of fibromyalgia is widespread pain.
- Can fibromyalgia cause brain fog?
Yes. Problems with concentration and memory are commonly described as “fibro fog”. Brain fog can also occur with B12 deficiency, thyroid disease, poor sleep, long Covid, ME/CFS and other conditions.
- Is there a blood test for fibromyalgia?
No. There is no specific blood test to diagnose fibromyalgia. Blood tests may be used to look for other conditions that can cause similar symptoms.
- Can B12 deficiency be mistaken for fibromyalgia?
Some symptoms can overlap, including fatigue, brain fog, pins and needles, mood changes and weakness. That does not mean B12 deficiency is always the cause, but it should be considered when the symptom pattern and risk factors fit.
- Can low iron make fibromyalgia symptoms feel worse?
Low iron or iron deficiency anaemia can cause tiredness, shortness of breath and palpitations, and some people also describe reduced stamina or feeling generally drained. If low iron is present alongside fibromyalgia, it may contribute to how unwell someone feels.
- Should I accept a fibromyalgia diagnosis?
Fibromyalgia is a recognised condition and the symptoms are real. But a diagnosis should not stop appropriate review if symptoms change, blood results are abnormal or there are signs that another condition may be contributing.
- How can B12 Metabolic Clinic help?
I provide GP-led assessment for people with symptoms such as fatigue, brain fog, pins and needles, dizziness, pain, palpitations and symptoms that have not been fully explained. I look at the whole picture, including B12, iron, folate, vitamin D, thyroid function, inflammation, risk factors and previous treatment response, before advising on the most sensible next step.
Book a GP-led assessment in Reading
If you have fibromyalgia symptoms, or you have been given a fibromyalgia diagnosis but feel something may still be missing, I can help you review the wider clinical picture.
At B12 Metabolic Clinic, I look at symptoms, medical history, risk factors, blood results, previous treatment response and possible cofactors such as B12, iron, folate, vitamin D, thyroid function and inflammation.
This is not about dismissing fibromyalgia. It is about making sure treatable deficiencies or metabolic issues are not overlooked.
