Why do I keep falling asleep during the day?

You sit down after lunch and the next thing you know, twenty minutes have gone. Or you nod off on the sofa by eight, on the train home, or in a meeting you actually cared about. You slept seven hours, so why does your body keep switching off?

Doctors call this excessive daytime sleepiness, and the plain answer is that it nearly always has a cause. The usual ones are sleep apnoea, iron deficiency, an underactive thyroid, depression, medicines and poor-quality sleep. A GP consultation with a few blood tests finds the answer for most people.

If you'd rather skip the reading, you can see a private GP at Harley Street for £150, with same-day appointments often available. For sleepiness that has dragged on without an obvious reason, our fatigue assessment looks further.

Is it normal to keep falling asleep during the day?

A dip in alertness in the early afternoon is normal. Your body clock produces a natural lull somewhere between about 1pm and 4pm, and a big lunch or a short night makes it deeper. Most adults need 7 to 9 hours of sleep a night to feel properly awake.

What isn't ordinary is falling asleep when you're trying to stay awake: mid-conversation, while reading, at the cinema, or behind the wheel. Microsleeps count too. Those are the few seconds where your head drops and you jolt back, often without realising you were gone.

Here is the one thing worth remembering. Tiredness is feeling drained; sleepiness is your brain actually tipping into sleep. Rest helps tiredness, but it rarely fixes sleepiness, because the problem is usually the quality of your sleep rather than the hours. If what you feel is more drained than drowsy, our guide to feeling tired all the time covers that side.

Often a partner notices first. You snore, you seem to stop breathing for a few seconds, you doze through every film. If you're reading this about someone else, those observations are exactly what a doctor wants to hear, so bring them to the appointment.

How sleepy are you? The Epworth score

Doctors measure daytime sleepiness with the Epworth Sleepiness Scale, a short questionnaire used across the NHS. It asks how likely you are to doze in eight everyday situations, such as reading, watching television, sitting as a car passenger for an hour or sitting quietly after lunch. Each one scores from 0 (would never doze) to 3 (high chance), giving a total out of 24.

How Epworth scores are usually read.

A score above 10 is worth discussing with a doctor. Bring your score with you: it gives the GP a starting point and a baseline to measure against once treatment begins.

Could sleep apnoea be causing my daytime sleepiness?

Obstructive sleep apnoea (OSA) is one of the most commonly missed causes. The throat muscles relax during sleep and narrow or block the airway. Each time, the brain briefly wakes you to reopen it, sometimes dozens of times an hour, so you can spend eight hours in bed and get very little deep sleep without knowing why.

NICE estimates that around 1.5 million UK adults have OSA, with many undiagnosed. Risk factors include being overweight, a large neck (over 43cm in men) and being male, though women are increasingly recognised as affected, particularly after the menopause. Classic signs are loud snoring, pauses in breathing that someone else notices, and waking with a dry mouth or headache. It's confirmed with an overnight sleep study arranged by a sleep specialist, and if your history points that way we can refer you.

Common causes of daytime sleepiness, at a glance.

Could low iron or an underactive thyroid explain it?

Low iron stores (ferritin) can cause fatigue even before haemoglobin drops to anaemic levels, and this is particularly common in women with heavy periods. A ferritin level below 30 µg/L can cause significant tiredness even when haemoglobin looks normal, and a simple blood test picks it up.

An underactive thyroid slows metabolism and brings fatigue, weight gain, cold intolerance and a foggy, slowed-down feeling. It affects around 2% of the UK population and is straightforward to diagnose with a TSH blood test. Our guide to thyroid symptoms and testing explains which profile fits.

Can depression make you sleep too much?

Yes. Depression is one of the leading causes of both fatigue and hypersomnia, which means sleeping too much. Some people with depression sleep 10 to 12 hours and still wake unrefreshed. If daytime sleepiness comes with low mood, loss of interest or poor concentration, depression should be considered alongside physical causes. Anxiety can also fragment sleep without cutting the total hours, which leaves you exhausted by day.

If you're unsure whether to start with a GP or a specialist, our article on seeing a GP or a psychiatrist walks through it.

Could my medication be making me sleepy?

Quite often, yes. Sedating antihistamines (the older hay fever and sleep remedies), some antidepressants, strong painkillers such as opioids, and some medicines for nerve pain, epilepsy or blood pressure all list drowsiness as a common side effect. Alcohol in the evening adds to the effect and fragments the second half of the night.

If the sleepiness began within a few weeks of a new medicine or a dose change, bring the packets to your appointment. Keep taking a prescribed medicine until you've spoken to a doctor, because there is often a simple swap or a change in timing.

Why am I so sleepy after a virus?

Flu, COVID-19 and glandular fever (Epstein-Barr virus) can leave people sleepy and slow for weeks after the infection itself has passed. For most, it lifts gradually. NICE describes symptoms that continue for more than 12 weeks after COVID-19, and can't be explained by anything else, as post-COVID-19 syndrome.

If you've been sleepy for more than four weeks since an illness, it's worth being checked. The fatigue assessment was designed with post-viral tiredness in mind and includes Epstein-Barr virus antibodies in its blood panel.

What about narcolepsy and idiopathic hypersomnia?

These are rarer, and they explain sleepiness that nothing else does. Narcolepsy is a long-term condition in which the brain can't regulate sleeping and waking properly. The signs are sudden sleep attacks, cataplexy (brief muscle weakness triggered by laughing, surprise or anger), sleep paralysis and vivid dream-like images as you fall asleep or wake.

Idiopathic hypersomnia looks different. People sleep long hours, often more than ten, wake groggy and confused for a long time, and find naps do little. Both conditions are diagnosed at a specialist sleep centre with an overnight study and daytime nap tests. If your story fits either, a GP can make the referral with the right detail attached.

What blood tests should I have for excessive sleepiness?

A useful baseline panel includes a full blood count for anaemia, ferritin for iron stores, thyroid function, blood glucose or HbA1c for diabetes, vitamin D and B12, and liver and kidney function. These cover the most common metabolic causes. If you want to arrange bloods on their own, our sister clinic Blood London offers a tiredness blood test panel.

When should I see a doctor about falling asleep during the day?

See a GP if you've been excessively sleepy for more than four weeks despite 7 to 9 hours in bed, if it's affecting work or driving, or if your Epworth score is above 10. See a doctor promptly if any of these apply:

• You've fallen asleep, or nearly fallen asleep, while driving.
• Sleepiness comes with sudden muscle weakness triggered by emotions, a possible sign of narcolepsy.
• You wake gasping or choking during the night.
• Your partner reports that you stop breathing during sleep.
• You have unexplained weight loss alongside the sleepiness.

If you feel sleepy while driving, stop somewhere safe. If you've been diagnosed with, or are being investigated for, sleep apnoea that causes excessive sleepiness, DVLA rules say you must not drive until your symptoms are controlled, and you may need to tell the DVLA. Your doctor will advise you.

How we can help

A private GP appointment at Harley Street is £150, with no fixed time limit, and is the natural first step. The GP takes a sleep history, works through your medicines, checks your Epworth score and decides which blood tests are worth doing. If sleep apnoea or narcolepsy is suspected, we can refer you to a sleep specialist.

For sleepiness that has lasted without an obvious cause, the fatigue assessment (£1,499) combines a full physical examination, a brain MRI at a partner imaging centre, a 12-lead ECG and a targeted blood panel. The panel covers full blood count and ESR, iron and ferritin, thyroid function, vitamin B12, folate and vitamin D, liver and kidney function, hormones, Epstein-Barr virus antibodies and coeliac screening. Blood results are typically ready within 3 to 5 working days and the MRI report within 7 to 10 working days, and your GP then reviews everything with you at a follow-up consultation. Where the tests find iron deficiency, a thyroid problem or a vitamin deficiency, treatment can often start as soon as the results are reviewed.