Tired despite enough sleep —
the causes nobody checks.

With entrepreneurs and executives the pattern looks almost identical every time. Seven to eight hours in bed, no sleep disorder in the narrow sense, no trouble staying asleep. And still the tank is empty by early afternoon, concentration drops away, and the evening is good for television and not much else.

They have long since seen a doctor. Blood count done, nothing remarkable. Then comes the sentence I hear regularly: so I suppose I have to live with it.

They do not. But the search almost always starts in the same wrong place, namely with the question of which value the lab might still be missing. Statistically the answer sits somewhere else, and that is the uncomfortable part.

Fatigue is not one state but three

Before causes, one distinction is worth making, and in consultations it almost always produces the first moment of clarity. Three very different states carry the same name in everyday language.

The first is sleepiness. You would fall asleep if you were allowed to, and sleeping makes it better. The second is exhaustion. You are physically empty, but sleep does not help, and often you cannot fall asleep at all. The third is loss of drive. The energy would be there, but you cannot reach it, and what used to pull you no longer pulls.

The S3 guideline describes exactly this: people use terms that can describe emotional, cognitive, physical and behavioural aspects, and a large number of biological, psychological and social causes come into question, often in combination. That is not an evasion, that is the starting position.

Which of the three states you are in shifts the whole direction of the search. Sleepiness despite adequate sleep duration points to disturbed sleep, not to short sleep. Exhaustion after exertion that lasts for hours or days is a warning sign in its own right. Loss of drive leads to a question many people never get asked.

One more thing belongs here for honesty's sake: often no definitive cause can be identified. The guideline says so itself. Anyone expecting a single clean explanation will frequently be disappointed.

The order almost nobody follows

Germany and Austria have a dedicated guideline for unexplained fatigue, the DEGAM S3 guideline on fatigue. It is freely available, an English short version exists, and in several places it contradicts what consumer articles on the topic say.

According to the guideline, the basic panel holds five items when there is no indication of a specific physical disorder: blood glucose, differential blood count, ESR or CRP, transaminases and gamma-GT, and TSH. Further laboratory or equipment-based diagnostics are only foreseen once the conversation or the examination has produced something concrete.

Ferritin, vitamin D and B12 are not on that list. That surprises many people, and it surprised me on first reading too. The reason is not that these values are irrelevant. The reason is that the guideline answers one question: are we missing an illness that needs treatment? For that, those five values are enough in the vast majority of cases.

The guideline is more pointed about the most common causes. At the top sit psychological disorders that need treatment, above all depression and anxiety, followed by medication side effects and substance use. Treatable serious physical illness is, in the guideline's words, rare and practically always accompanied by abnormalities in the history or the physical examination.

Two questions that settle more than half the cases

For suspected depression the guideline gives two screening questions, referring to the past four weeks. Have you often felt down, dejected or hopeless? Have you had little interest or pleasure in doing things? If both are answered with no, significant depression can be considered ruled out with high confidence.

That is remarkably simple, and that is exactly why it gets skipped. Nobody goes to the doctor with the feeling that they might be depressed. They go with the feeling of being tired, and they expect an answer from the lab.

Four fallacies the guideline names itself

The most interesting part of the document is a short list of typical errors. It describes rather precisely what goes wrong in practice.

When the sleep is there but does not work

One cause fits the title of this article exactly and still gets missed regularly. With sleep apnoea syndrome the sleep duration is fine. The person lies in bed for eight hours and does sleep. That sleep is simply interrupted hundreds of times a night without them noticing.

The scale is considerable. A 2019 analysis in The Lancet Respiratory Medicine estimated that around 936 million adults aged 30 to 69 worldwide have mild to severe obstructive sleep apnoea, of whom roughly 425 million have it in moderate to severe form. The authors describe this as an estimate based on existing literature rather than a measured figure. That a large share of it is never diagnosed is the uncontested part.

The guideline lists sleep apnoea syndrome among the courses you must not miss, and gives two screening questions: is there loud snoring or are there observed breathing pauses during sleep? Does unintended falling asleep occur during the day in situations where it should not?

The catch in the first question is obvious. Anyone sleeping alone cannot answer it. Anyone living with someone should not ask themselves but the person next to them. In practice that is the fastest and cheapest diagnostic step available on this topic.

How strongly disturbed sleep drags the hormonal picture with it is covered through the example of night-time cortisol under lowering cortisol at night.

Where the guideline ends and optimisation begins

This is where it gets contradictory, and I consider the contradiction the most important part of the article.

The guideline answers whether an illness requiring treatment is being missed. It does not answer why somebody in good health is not as capable as they could be. Those are two different questions, and they need different tools.

One example shows both sides. In a randomised trial in the BMJ, 144 women with unexplained fatigue but without anaemia received iron or placebo for four weeks. Fatigue fell by 29 per cent in the iron group compared with 13 per cent on placebo. The decisive part is the authors' qualification: only the women with a ferritin of 50 micrograms per litre or below improved.

So iron can indeed be the reason, even without anaemia. But not in everybody, and not as a default answer. That is precisely what the guideline warns about in its first fallacy: a value on its own is not yet an explanation. It becomes one when it fits the picture.

What a full blood count actually contains and what is systematically missing from it is broken down under the blood panel and vitamins. And why single values without context rarely tell you much is placed in a wider frame under longevity.

In practice this means a clear order. First the guideline question: is something behind this that needs treatment? That belongs in medical hands, completely. Only once that is settled does the second question make sense: what is holding you back in daily life even though you are not ill? For that you need training history, sleep behaviour, nutrition and test results on one table, and that is the framework of a structured assessment.

What you can check before booking an appointment

The points below do not replace a medical assessment. They do make the appointment shorter and better, because you walk in with observations rather than a feeling.

For fourteen days, write down when you go to bed, when you get up and how you hold up through the day. Alongside that, these five points:

• Medication. The guideline lists side effects among the most common causes. Beta blockers, antihistamines, some antidepressants and sleeping tablets sit high on that list. Take the full list to your appointment, including anything over the counter.
• Alcohol in the evening. It shortens the time to fall asleep and dismantles the second half of the night. Two weeks without is the most honest test available.
• Caffeine after midday. Topping up in the afternoon to get through is paid for in the evening. That turns into a loop that sustains itself quickly.
• Training load. Add up every session of the week, travel time included. Too much load with too little recovery feels from the inside exactly like a nutrient problem. More on that under recognising overtraining.
• Food across the day. Anyone who has had nothing but coffee until 3 p.m. need not wonder about an afternoon slump. It sounds banal and it is. It still shows up in every second log I read.

That adding up your own week rarely produces enthusiasm is part of the procedure. In many cases the answer is in the calendar, not in the lab.

The fourth point deserves a note. A worsening that sets in hours after exertion and lasts for days is called post-exertional malaise and is the cardinal symptom of ME/CFS. It is regularly mistaken for poor conditioning, and the advice to simply do more sport is not harmless in that case. Anyone who recognises this in themselves belongs in expert hands before anybody writes a training plan.