Knowledge Centre
Providing rapid medical guidance and expert health insights for informational purposes. While our guides are written by Harley Street clinicians, they do not replace a professional consultation.
Excessive Daytime Sleepiness
Excessive daytime sleepiness (EDS) means feeling an overwhelming urge to sleep during waking hours, even after a full night's rest. It affects an estimated 10-20% of the UK adult population to some degree. The cause is not always obvious, which is why many people live with it for months or years before seeking help.
EDS is a symptom, not a diagnosis. Finding out what's behind it — whether that's a sleep disorder, a nutritional deficiency, a thyroid problem, or something else — is the key to fixing it.
Seek urgent medical advice if:
- You've fallen asleep or nearly fallen asleep while driving
- Sleepiness is accompanied by sudden muscle weakness triggered by emotions (possible narcolepsy)
- You wake gasping or choking during the night
- Your partner reports that you stop breathing during sleep
- You have unexplained weight loss alongside fatigue
Falling asleep at the wheel is a medical emergency risk. The DVLA requires you to stop driving and notify them if you have confirmed untreated sleep apnoea.
Common causes
Obstructive sleep apnoea (OSA)
OSA is the most commonly missed cause of EDS. The throat muscles relax during sleep, narrowing or blocking the airway. This causes repeated micro-awakenings that fragment sleep without the person realising it. NICE estimates 1.5 million UK adults have OSA, with many undiagnosed. Risk factors include being overweight, having a large neck circumference (over 43 cm in men), and being male — though women are increasingly recognised as affected, particularly after menopause.
Iron deficiency and anaemia
Low iron stores (ferritin) cause fatigue even before haemoglobin drops to anaemic levels. This is particularly common in women with heavy periods. A ferritin level below 30 µg/L can cause significant tiredness, even if your haemoglobin is technically "normal." A simple blood test picks this up.
Hypothyroidism
An underactive thyroid slows metabolism and causes pervasive fatigue, weight gain, cold intolerance, and cognitive sluggishness. It affects about 2% of the UK population and is straightforward to diagnose with a TSH blood test.
Depression and mental health
Depression can cause both insomnia and hypersomnia. Some people sleep excessively but feel unrefreshed. Anxiety disorders can fragment sleep quality without reducing total sleep time, leading to daytime exhaustion that the patient attributes to physical causes.
Poor sleep hygiene
Irregular sleep schedules, screen use before bed, caffeine after midday, and alcohol (which fragments REM sleep) are surprisingly common contributors. Before investigating medical causes, it's worth honestly assessing sleep habits.
Diagnosis
The Epworth Sleepiness Scale (a short questionnaire scoring your likelihood of dozing in various situations) is a useful starting point. A score above 10 out of 24 suggests clinically significant sleepiness.
Blood tests form the backbone of initial investigation: full blood count, ferritin, thyroid function, vitamin B12, vitamin D, HbA1c (diabetes screen), and liver and kidney function. These cover the common metabolic and haematological causes.
If OSA is suspected, a home sleep study (pulse oximetry or a portable polygraphy device worn overnight) can confirm the diagnosis without needing a hospital stay.
How we can help
We offer a focused fatigue assessment that includes a GP consultation and a comprehensive blood panel covering the causes listed above. Results are typically available within 24-48 hours, and your GP will contact you to discuss findings and next steps.
If a sleep study is needed, we can arrange a home sleep test or refer to a sleep specialist. For conditions identified through blood tests — iron deficiency, thyroid problems, vitamin deficiencies — treatment can often begin the same day.
Fatigue assessment with blood tests
GP consultation plus comprehensive blood panel. Results within 24-48 hours. No referral required.
Call 020 7499 1991 or book online.
Dr Mohammad Bakhtiar
Health Screening and Men's Health • GMC 4694470
"Leading our clinical team, Dr Bakhtiar has been seeing patients at Medical Express Clinic for over 20 years. Patients regularly praise his expertise in comprehensive health assessments, sexual health screening, diagnosis and treatment as well as his personable and compassionate approach to care."
View TeamCommon Questions
Q.What's the difference between tiredness and excessive daytime sleepiness?
Tiredness is a general feeling of fatigue that can improve with rest. Excessive daytime sleepiness (EDS) is a persistent, overwhelming urge to fall asleep during the day, even after what seems like adequate nighttime sleep. If you're falling asleep in meetings, while watching television, or — more concerning — while driving, that's EDS, not ordinary tiredness.
Q.Could sleep apnoea be causing my daytime sleepiness?
It's one of the most common causes. Obstructive sleep apnoea (OSA) causes your airway to repeatedly collapse during sleep, disrupting rest without you necessarily being aware of it. Classic signs include loud snoring, witnessed pauses in breathing, and waking with a dry mouth or headache. A home sleep study can confirm or exclude it.
Q.What blood tests should I have for excessive sleepiness?
A useful baseline panel includes a full blood count (to check for anaemia), ferritin (iron stores, which can be low even when haemoglobin is normal), thyroid function tests (hypothyroidism causes fatigue), blood glucose or HbA1c (for diabetes), and vitamin D and B12 levels. These cover the most common metabolic causes of persistent fatigue.
Q.Can depression cause excessive sleepiness?
Yes. Depression is one of the leading causes of both fatigue and hypersomnia (sleeping too much). Some people with depression sleep for 10-12 hours and still feel unrefreshed. If daytime sleepiness is accompanied by low mood, loss of interest in activities, or difficulty concentrating, depression should be considered alongside physical causes.
Q.When should I see a doctor about daytime sleepiness?
See a doctor if you've been excessively sleepy for more than four weeks despite getting 7-9 hours of sleep, if sleepiness is affecting your work or driving, or if you have associated symptoms like snoring, morning headaches, or unintentional weight gain. A single consultation with blood tests can often identify the cause.
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