Fatigue is one of the more workable problems we see, and the reason is straightforward: it almost always has a cause, and causes can be found. The people who get furthest with persistent tiredness are the ones whose fatigue was properly worked up before anyone started treating it.
That order is the point of this article. Fatigue is the symptom most likely to be treated before it is understood, and the one where doing so wastes the most time.
So here is what we look for, in roughly the order we look for it.
Fatigue is a symptom, not a diagnosis
“Fatigue” covers several different experiences that happen to share one word. Sleepiness — the sense that you could fall asleep sitting up — points somewhere different from heaviness in the limbs, which points somewhere different from the mental flatness where the body could continue but the drive to start anything is gone. Post-exertional symptoms, where the bill for yesterday’s effort arrives a day or two later, are different again.
The first useful thing in any appointment about fatigue is pinning down which of those you actually have, when it started, what makes it better or worse, and what you have stopped doing because of it. That last list is usually the most informative part of the conversation, and it is also the thing we measure progress against later.
The sleep question comes first
Most persistent daytime fatigue has something to do with sleep, and a surprising amount of it has to do with sleep that looks adequate on paper.
We ask about quantity and timing, but we are more interested in quality and continuity: how long it takes to fall asleep, how often you wake, whether you wake unrefreshed after a full night, whether anyone has mentioned snoring or pauses in your breathing, and whether you doze off in the afternoon without intending to.
Obstructive sleep apnoea is common, frequently missed, and treatable, and it is worth ruling in or out early rather than late. Shift work, an irregular schedule, evening alcohol and a bedroom that is too warm or bright all damage sleep continuity, and all are modifiable. Insomnia that has become a pattern of its own responds well to cognitive behavioural therapy for insomnia, which has better long-term results than sleeping tablets.
None of that is glamorous. It is, however, where the largest share of recoverable daytime energy sits.
The bloodwork worth doing
A short list of blood tests genuinely changes what happens next; a long list mostly produces reassurance and a bill.
The short list: a full blood count for anaemia, ferritin for iron stores (which can be low enough to cause symptoms while the blood count still reads normal), thyroid function, HbA1c or fasting glucose, kidney and liver function, calcium, vitamin B12 and vitamin D. Coeliac serology where the history fits. Inflammatory markers where there is a reason to look for inflammation.
That panel catches most of the common, correctable medical causes. A normal result does not mean nothing is wrong — it means the search moves to sleep, medication, activity, pain and mood rather than repeating the same tests.
Medications and the ordinary things
Before anything else gets added, it is worth subtracting. Beta blockers, antihistamines, several blood pressure medications, opioids, gabapentinoids, some antidepressants and a number of over-the-counter sleep aids all cause daytime tiredness, and people are often taking two or three of them at once without having connected any of them to how they feel.
Alcohol fragments sleep even in modest amounts, and late caffeine does the same less obviously. Dehydration, skipped meals and a diet that has quietly narrowed are all worth asking about.
Pain that fragments the night
This is the overlap we see most often in our own clinic. A painful shoulder, knee, neck or heel that wakes someone two or three times a night produces exactly the daytime picture people describe as fatigue — and it tends to be attributed to anything other than the joint, because the joint is what hurts during the day.
Where that is the pattern, treating the pain is part of the sleep plan rather than a separate project. The evidence we have for photobiomodulation sits here, in joint and tendon problems, and that is where we use it: pooled randomised trials show pain reduction in neck pain that persisted at follow-ups up to 22 weeks after treatment ended, and in shoulder tendinopathy at 20.41mm on a 100mm scale as a standalone treatment and 16.00mm alongside an exercise programme.
We are careful about the direction of that claim. What those trials measured is pain. We are not presenting them as sleep trials or as fatigue trials, and we do not treat fatigue by treating a joint unless a painful joint is plausibly part of what is interrupting the night.
Activity, pacing and the crash cycle
Deconditioning is a real contributor and a delicate subject, because telling a tired person to exercise is usually unhelpful and occasionally harmful.
The useful version is specific. Where fatigue is not accompanied by post-exertional worsening, a graded, genuinely gradual increase in activity from whatever the current baseline actually is tends to improve energy over weeks. Where there is post-exertional worsening — where effort today reliably produces a worse day after tomorrow — pushing through does damage, and pacing within a sustainable envelope is the correct approach instead. Getting that distinction right at the start matters more than any treatment choice that follows.
When fatigue needs assessment sooner
Some features move fatigue up the queue: unintentional weight loss, fevers or night sweats, new lumps or swollen glands, breathlessness or chest pain, blood loss from any source, new neurological symptoms, fatigue that is worsening quickly, or fatigue that began abruptly in someone who was previously well. Fatigue following an infection also deserves a proper assessment rather than a label.
If any of those apply, see your physician promptly rather than read further.
Where photobiomodulation fits
Of the conditions where photobiomodulation has been studied for fatigue specifically, the strongest signal is in fibromyalgia.
A 2025 umbrella review in Systematic Reviews pooled 15 meta-analyses covering 204 randomised controlled trials and more than 9,000 participants, across 35 health endpoints in 15 conditions, and graded the certainty of the evidence behind each. Fibromyalgia fatigue came out as one of only five endpoints supported by moderate-certainty evidence, at an equivalent standardised mean difference of 1.25 (95% CI 0.63 to 1.87), and the authors name fibromyalgia first among the best-supported conditions.
That is a real finding and worth knowing about. It is also worth being precise about what sits around it: in that same review most of the other 35 endpoints were graded low or very low certainty, and the authors’ own conclusion is that further high-quality trials and standardisation of treatment protocols are needed before widespread clinical adoption. This is an adjunct with modest, real effects in the conditions where it has been studied properly — it runs alongside the sleep, medication, pain and activity work rather than replacing any of it, and we are not citing a device clearance for this use.
What “brain fog” has to do with it
Most people who come in about fatigue also describe difficulty concentrating, and the two are worth separating because they are measured differently and the evidence behind them is different.
For cognitive performance, a 2025 systematic review and meta-analysis in Lasers in Medical Science pooled 24 randomised trials with 820 participants and found a benefit for global cognitive function at a standardised mean difference of 0.66 (95% CI 0.23 to 1.08, P=0.003). An earlier randomised controlled trial of 40 volunteers found improved reaction time on a sustained-attention task and improved memory-task performance, with self-reported affect still improved at two weeks.
Those are cognitive-performance findings from cognitive-performance trials, and that is the only way we use them. The umbrella review above graded cognitive function at a smaller effect than its fibromyalgia fatigue figure — separate questions with separate answers.
What a first visit looks like
We take the history properly, which takes longer than people expect. We screen sleep, including for apnoea. We review every medication and supplement you take. We look at the short blood panel if it has not been done recently. We examine whatever hurts. We ask what you have stopped doing, and we write down a baseline we can compare against.
Then we decide what to address first, and we say in advance what would count as this not working and when we will check.
What we do not use it for
Light therapy at our clinic is used for musculoskeletal pain and for cognitive performance. Mood disorders are managed by your own physician or a mental-health clinician, and we refer rather than treat. Fatigue with an identified medical cause is treated by addressing that cause, and the treatments described here are not a substitute for doing so.
This article is general education, not medical advice, and it is not a substitute for evaluation by a qualified clinician. It does not establish a physician–patient relationship. Individual results vary, and the studies described report group averages rather than what any one person should expect. Treatments discussed may not be FDA-cleared or approved for the conditions mentioned; where that is the case it is stated in the text. Talk to your own physician before starting, stopping or changing any treatment.
Son 2025 — PMID 40770824 · Zhu 2025 — PMID 40394373 · Barrett 2013 — PMID 23200785 · Chow 2009 — PMID 19913903 · Haslerud 2015 — PMID 25450903
