In short
- Duration classifies it. Up to a month is acute, one to six months subacute, beyond six months chronic.
- A cause is found in about two thirds of people with chronic fatigue. The rest need a different kind of plan.
- The history does the work, not the panel. In one study, laboratory tests clarified the cause in only 5 percent of cases.
- Big panels cause harm. Testing without a reason produces false positives and months of chasing findings that never mattered.
- Medication is a frequent culprit. Beta blockers, antidepressants, sedating antihistamines, opioids and gabapentinoids all do this.
Condition Overview
First, what do you actually mean by tired?
The word covers four different things, and separating them narrows the field immediately.
- Difficulty starting activity, a subjective sense of weakness.
- Reduced capacity to keep going, easy fatigability.
- Mental fatigue, concentration, memory and emotional stability.
- Sleepiness, an uncontrollable need to sleep, which is a different problem with a different work up.
Duration matters
| Category | Duration | What it usually means |
|---|---|---|
| Acute | Up to one month | Usually an identifiable illness or a recent life stressor. Little or no testing needed |
| Subacute | One to six months | Warrants a structured work up |
| Chronic | Over six months | Structured work up, and a plan that continues even if no cause is found |
A clue most people miss
How the fatigue behaves points to the type of cause.
- Fatigue tied to activity, where you notice it because of what you can no longer complete, more often reflects an underlying medical condition.
- Fatigue that is constant, unrelated to exertion and not improved by rest, more often reflects a psychological cause, a medication or substance use.
The realistic list of causes
- Cardiopulmonary. Heart failure, chronic lung disease, sleep apnoea.
- Endocrine and metabolic. Under or overactive thyroid, kidney or liver disease, adrenal insufficiency, electrolyte problems.
- Blood. Anaemia, and iron deficiency even without anaemia.
- Infection. Glandular fever type illness, viral hepatitis, HIV, tuberculosis.
- Rheumatological. Fibromyalgia, polymyalgia rheumatica, lupus and related conditions.
- Psychological. Depression and anxiety disorders, which are common and treatable.
- Medication. Benzodiazepines, antidepressants, muscle relaxants, first generation antihistamines, beta blockers, opioids and gabapentinoids.
- Substances. Alcohol above all.
The uncomfortable truth about blood tests
Broad testing without a suggestive history has a low yield. In a prospective study of 100 adults with fatigue lasting at least a month, laboratory studies clarified the cause in only 5 percent of cases.
Worse, minor abnormal results were common and did not change outcomes. Ordering tests with a low prior probability generates false positives, which lead to more tests, more waiting and more worry for findings that were never going to matter.
So the panel here is deliberately targeted, and it is the history and examination that do most of the work.
What is actually tested
- Full blood count with differential.
- Chemistry including glucose, electrolytes, calcium, kidney and liver function.
- Thyroid stimulating hormone.
- Creatine kinase, if there is muscle pain or weakness.
- Ferritin, with a low threshold for checking it.
- Age and sex appropriate cancer screening brought up to date.
Not routinely done without a reason: Epstein Barr and other viral serologies, Lyme testing, autoimmune panels, immunoglobulins, broad vitamin screens, coeliac testing or imaging. Those are ordered when something in the history or examination points to them.
When to See a Doctor
- Your energy has been reduced for more than a few weeks and rest does not restore it.
- Your training performance or work output has declined without a change in effort.
- You snore, wake unrefreshed or feel sleepy during the day, which suggests sleep apnoea.
- You have been told your blood tests are normal but you do not feel normal.
- You started a new medicine around the time the fatigue began.
- You have unintended weight loss, night sweats, fever or bleeding alongside the fatigue, which need prompt diagnostic investigation.
- You have persistent low mood, loss of interest or thoughts of harming yourself, which need care from a psychiatrist or psychologist rather than a performance programme.
How Dr. Felix Assesses This
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1
Goals and history
When the decline started and how it behaves across a day and a week, your sleep and snoring, workload and travel, alcohol, mood, training, diet, medical and family history, and every medicine and supplement.
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2
Medical review
Examination, blood pressure, body composition, and blood work covering full blood count, iron studies, ferritin, glucose and HbA1c, kidney, liver and thyroid function, vitamin D and B12, inflammatory markers, and testosterone in men where symptoms justify it.
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3
Suitability decision
Dr. Felix explains what the results show, whether a cause has been identified, whether a sleep study or specialist referral is needed, and which contributors are medical rather than lifestyle. Overlapping causes are common.
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4
Personal plan
Treatment for whatever is found, a written plan covering sleep, training load, protein, alcohol and workload, referral where a psychological or specialist assessment is the right step, and a dated review to check the response.
Treatment Options
Performance Longevity Program
Where does more training stop helping? The dose response curve is real but it is not a straight line. In…
View Treatment
Longevity Consultation
What happens in the appointment? Roughly half of it is history. What you do, how you sleep, how much you…
View Treatment
Precision Medicine Program
What does precision actually mean here? Three concrete things: using a risk model that fits you, adding the factors your…
View Treatment
Why Early Treatment Can Matter
Most of the causes here are straightforward to treat once identified, and several correct within weeks. Iron deficiency, vitamin D deficiency and thyroid dysfunction all respond well. Sleep apnoea treated early spares years of daytime fatigue and cardiovascular strain.
Left unexplained, fatigue tends to reshape everything around it: training stops, weight rises, sleep worsens and the original cause becomes harder to see under the consequences. Investigating it while the picture is still simple makes the consultation considerably more productive.
Why Early Treatment Can Matter
Most of the causes here are straightforward to treat once identified, and several correct within weeks. Iron deficiency, vitamin D deficiency and thyroid dysfunction all respond well. Sleep apnoea treated early spares years of daytime fatigue and cardiovascular strain.
Left unexplained, fatigue tends to reshape everything around it: training stops, weight rises, sleep worsens and the original cause becomes harder to see under the consequences. Investigating it while the picture is still simple makes the consultation considerably more productive.
Many causes correct fast
Iron, thyroid and vitamin D problems often improve within weeks of treatment.
Consequences pile up
Untreated fatigue reduces activity, worsens sleep and obscures the original cause.
One assessment, one answer
A properly chosen panel usually beats repeated minimal tests over months.
Cost & Consultation Investment
The consultation is long because the history matters as much as the tests, and the laboratory panel is broader than a routine screen for the same reason. What follows depends on what is found, whether a sleep study or referral is needed, and how much follow up the treatment requires. Current figures are on the pricing page.
Frequently Asked Questions
Up to a month is acute and usually explained by an illness or a life stressor, needing little evaluation. One to six months is subacute and six months or more is chronic, and both warrant a structured work up.
Usually not. In a study of 100 adults with fatigue for at least a month, laboratory tests clarified the cause in only 5 percent. Minor abnormal results were common and did not change outcomes. The history and examination do most of the work.
Because testing without a reason produces false positives, and each one leads to more tests, more waiting and more worry over findings that never mattered. Viral serologies, autoimmune panels and broad vitamin screens are ordered when something points to them.
Full blood count, chemistry including glucose, electrolytes, calcium, kidney and liver function, thyroid stimulating hormone, ferritin, and creatine kinase if there is muscle pain or weakness. Cancer screening appropriate to your age and sex is brought up to date.
Frequently. Beta blockers, antidepressants, benzodiazepines, muscle relaxants, first generation antihistamines, opioids and gabapentinoids all cause fatigue. A complete medication list including over the counter products is reviewed.
Partly by the pattern. Fatigue linked to activity, where you notice it through what you cannot complete, more often reflects a medical condition. Constant fatigue unrelated to exertion and not improved by rest more often reflects mood, medication or substance use.
That happens in about a third of chronic cases and it is not a dismissal. You get scheduled short appointments, reassessment at one to three months with tests repeated, and treatment aimed at symptoms rather than being sent away.
A trial is reasonable where there are depressive symptoms, even short of a formal diagnosis, and it has been used effectively in unexplained symptoms. It takes several weeks to judge and is stopped after two months at a proper dose if it has not helped.
Not used. They do not address the cause and are not part of the recommended approach for unexplained fatigue.
Graded exercise therapy and cognitive behavioural therapy showed comparable results in a randomised primary care trial of patients with more than three months of unexplained fatigue. Which one is used depends on your preference.
It is associated with higher mortality. In a cohort of 18,101 people followed for an average of 16.6 years, the highest fatigue quartile had a 40 percent higher risk of death, driven by cardiovascular causes. That is one reason it is investigated rather than accepted.
It depends on how wide the work up needs to be, so a single figure would be misleading. You get the full cost in the consultation before anything is arranged.
Evidence
Where this information comes from
Every figure on this page is taken from the sources below. All of them are free to read, so you can check them yourself.
This page is general medical information and does not replace a personal consultation. Trial results are averages across large groups, not a prediction for any one person.