Why am I always tired? Fatigue, post-viral fatigue and post-exertional malaise

A 2023 review for family doctors sorts fatigue into three groups (American Family Physician, 2023):

• Physiologic fatigue tracks sleep, diet and the balance between effort and rest, and it responds to changes in them.
• Secondary fatigue comes from an underlying condition and improves with treatment of that condition. Laboratory tests help rule out conditions that present with fatigue, such as anemia and thyroid disease (American Family Physician, 2023).
• Chronic fatigue persists, and it includes ME/CFS. In 2021 and 2022, 1.3% of US adults had ME/CFS, women more than men (CDC, NCHS Data Brief 488).

Asking why you are always tired is the right question, and a good answer starts with a careful history: how you sleep, what you eat, what you take, what changed before the tiredness began and how it responds to rest. Our guide to blood tests for fatigue and low mood covers the first round of tests.

Part of the answer comes from the immune system. During an infection, immune cells release cytokines that act on the brain and produce sickness behaviour, a set of changes that includes fatigue, malaise, disturbed sleep and poor concentration (Brain, Behavior, and Immunity, 2003). A 2008 review describes how immune signalling that continues, as in long infections or autoimmune disease, can deepen these effects (Dantzer et al., 2008).

Two patterns deserve their names:

• Post-viral fatigue follows an infection and outlasts it. The CDC lists tiredness or fatigue that interferes with daily life among the common symptoms of long COVID (CDC), and in 280 adults after SARS-CoV-2 infection, antibody evidence of recent Epstein-Barr virus reactivation went with long COVID with fatigue (Peluso et al., 2023). Our piece on post-viral fatigue symptoms goes further.
• Post-exertional malaise (PEM) is a worsening of symptoms after even minor physical or mental exertion that the person would have tolerated before (CDC). The 2015 criteria for ME/CFS require it, along with fatigue lasting more than six months and unrefreshing sleep (CDC).

Researchers study several mechanisms behind lasting fatigue, and no single one explains every case. The guide to malaise covers the wider feeling of being unwell that travels with it.

Blood tests for fatigue look for treatable causes. The CDC's guidance for clinicians evaluating ME/CFS lists the basic screening involved: a complete blood count with differential, electrolytes, glucose, kidney and liver tests, thyroid tests, ESR, CRP and urinalysis, among others. Guidance for family doctors favours tests chosen by the history and examination, and notes that testing without specific indications changes management in about 5% of patients (American Family Physician, 2023).

A normal set of results matters: it makes the common causes less likely. It leaves most immune signalling unmeasured, and it cannot confirm ME/CFS, which has no validated diagnostic biomarker (BMC Medicine, 2023). The CDC notes that routine blood tests may be normal in someone with long COVID (CDC). Our guides to chronic fatigue blood tests and to online chronic fatigue tests versus blood tests explain what each can show.

For fatigue that outlasts normal results, a broad panel measures the immune and inflammatory proteins a routine workup leaves out: cytokines such as IL-6, IL-1β and TNF-α, interferons such as IFN-γ, chemokines such as IP-10, and markers such as GDF-15 and FGF21. The panel places each against a healthy reference, and a retest shows which way each moves. Beside an activity and symptom diary, that gives you and your doctor objective data about a symptom that is hard to measure.

An activity and symptom diary makes any test more useful. Note what you did each day, how you slept and how you felt that day and the next two; the record shows whether effort on one day comes back as worse symptoms later, which is the pattern of post-exertional malaise.

A panel cannot measure how tired you are, diagnose ME/CFS or long COVID, or choose a treatment. Group differences in research say nothing certain about one person.

Mune Mirror™^* is currently in development, and the performance characteristics of this test have not yet been established. It is investigational. It does not diagnose, detect, screen for, treat, cure or prevent any disease. Results are for research and informational purposes, to discuss with your own doctor.

The guide to unwellness testing explains how this kind of measurement fits beside standard care.

Mune Mirror™ measures more than 1,000 immune and inflammation proteins from an at-home sample, benchmarks each against a healthy reference and repeats the measurement over time. For fatigue that has outlasted a normal workup, it gives you a measured record to set beside your activity and symptom diary and bring to your doctor. It does not explain your fatigue or diagnose a condition.

Why am I always tired even after sleeping?

Tiredness that sleep does not relieve has many possible causes, from sleep disorders and lifestyle strain to conditions such as anemia or thyroid disease. Unrefreshing sleep is one of the required symptoms of ME/CFS under the 2015 criteria. A doctor can sort out which pattern fits and which tests make sense.

What is post-exertional malaise?

The CDC defines post-exertional malaise as a worsening of symptoms after even minor physical or mental exertion that a person would have tolerated before. The 2015 criteria for ME/CFS require it, and the CDC lists symptoms that get worse after effort among the signs of long COVID.

What is post-viral fatigue?

Post-viral fatigue is tiredness that follows an infection and outlasts it. The CDC lists fatigue that interferes with daily life among the common symptoms of long COVID, and the 2024 National Academies definition of long COVID names ME/CFS among the conditions it can include.

What blood tests check for the causes of fatigue?

Typical first tests include a complete blood count, a metabolic panel with glucose, kidney and liver tests, thyroid tests, and inflammation markers such as ESR and CRP, chosen by your doctor from your history and examination. These look for treatable causes such as anemia or thyroid disease.

When should tiredness send me to a doctor?

See a doctor if tiredness lasts for weeks, limits daily life, gets worse, or arrives with new symptoms such as weight loss, fever or breathlessness. Sudden or severe symptoms need urgent care.