Ajax Harwood Clinic
ME/chronic fatigue syndrome
ME/CFS is a long-term condition whose central feature is not tiredness but a delayed crash after exertion — physical, mental or emotional effort is followed hours or days later by a worsening of symptoms out of all proportion to what was done, and it can take days or weeks to settle.
Get help straight away if
These are uncommon, but they need same-day care — go to an emergency department, do not wait for an appointment.
Contact us promptly if
Not an emergency, but worth being seen sooner rather than waiting it out.
- New weakness, numbness, or problems with speech or vision
- Fever, night sweats, or losing weight without trying
- Fainting, rather than feeling faint
What usually happens
The delayed crash after exertion is the defining feature, and it is what separates this from ordinary fatigue or from being unfit. If effort today makes you worse the day after tomorrow, that is the pattern we are looking for, and it is worth describing carefully.
Because of that, advice to push through is not just unhelpful here but can cause lasting harm. Exercise programmes that increase activity on a fixed schedule regardless of the crash have made people substantially worse, and we do not use that approach.
The approach instead is pacing — finding the level of activity you can sustain without triggering a crash, and staying inside it, including on good days. Good days are where most crashes are made.
Normal test results are expected. As with several conditions we see, there is no test that confirms it; tests are done to exclude other explanations, and coming back normal is part of the process rather than a dead end.
Many people with ME/CFS feel considerably worse standing up — light-headed, foggy, heart racing. That is a recognised and often treatable part of it, so it is worth mentioning even though it can sound unrelated.
At your appointment
We will ask specifically about the crash: what brings it on, how long the delay is, how long it lasts, and what it feels like. That history does more diagnostic work than any test.
A focused set of blood tests to exclude the conditions that can present as long-standing fatigue, rather than an open-ended search.
A conversation about pacing and about tracking activity, so decisions are based on your pattern rather than on a general schedule.
We will look for the treatable things that travel alongside it — disturbed sleep, symptoms on standing, pain, and low mood where it is present.
Should I be tested?
Last reviewed 2026-09-23
"Should I be tested?" for ME/CFS
You may want a blood test to prove ME/CFS is real. There isn't one. ME/CFS is diagnosed from your symptoms, not a lab result. The key sign is a crash after activity, hours or days later. This crash lasts longer than you'd expect. Poor sleep that doesn't refresh you is another sign. Trouble thinking clearly, or feeling worse standing up, can happen too. We still run a set of blood tests. These check for other causes of fatigue, like thyroid problems or anemia. Normal results don't mean nothing is wrong. They help rule out other causes, so we can focus on the right plan for you.
Tests you may hear about
- • Complete blood count (CBC)
- • Electrolytes (sodium, potassium, chloride, bicarbonate)
- • Kidney function (creatinine/eGFR, BUN, urine albumin-to-creatinine ratio)
- • Liver panel (ALT, AST, GGT, ALP, bilirubin, albumin)
- • TSH (thyroid stimulating hormone)
- • HbA1c and fasting glucose (diabetes screening)
- • Ferritin
- • Celiac serology (tTG-IgA + total IgA)
- • Vitamin B12 (cobalamin)
- • Folate (serum and RBC folate)
- • Vitamin D, 25-hydroxy (25-OH vitamin D)
Popular labels: what they mean
"Chronic EBV" / "reactivated Epstein-Barr" as a cause of fatigue
Not a recognized medical diagnosis — here’s what it usually means and what to ask about instead.
You may have heard that 'chronic' or 'reactivated' Epstein-Barr virus (EBV) explains your tiredness. EBV is the virus behind mono. Over 90 percent of adults have had it, often without knowing. Once infected, your blood carries EBV antibodies for life. A positive antibody test does not mean the virus reactivated. It just shows a past infection, like almost everyone has. There are two real, separate EBV illnesses. One is mono itself: a short illness with fever and a sore throat. The other is a very rare condition called chronic active EBV disease. It causes ongoing fever and organ problems, and needs a specialist right away. Your tiredness is real. It's just very unlikely to come from an old EBV infection showing up on a blood test.
Worth asking
- How do I work out where my limit actually is?
- What should I do during and after a crash?
- Could my symptoms on standing be treated?
- What support can you help me get for work or study?
Curious what your doctor is weighing up? The clinical tool we use for ME/chronic fatigue syndrome is open to anyone — it is detailed and written for clinicians, and you are welcome to read it.
Open the clinician reference →General health information for Ajax Harwood Clinic patients and the public — not medical advice, and not a substitute for seeing your own doctor. In an emergency call 911.