Why am I tired even after 8 hours of sleep?

Hours in bed aren't the same as good sleep. If your sleep is fragmented — by an unsupportive mattress, a too-warm room, alcohol, or an undiagnosed issue like sleep apnoea — you can spend eight hours in bed and still wake unrefreshed. If your sleep environment and habits are good and you're still exhausted, that's a strong reason to see your GP, because the cause may be physical: low iron, low vitamin D, an underactive thyroid and others all cause tiredness and are easily tested for.

Could I be low in vitamin D?

In Ireland, quite possibly. Because of our northern latitude, the sun is too weak from around October to March for your skin to make vitamin D — a 'vitamin D winter' — and roughly half of Irish adults are deficient in wintertime. The HSE recommends most adults take a 15 microgram vitamin D supplement daily. Low vitamin D is linked to tiredness and low mood, so it's well worth discussing with your GP or pharmacist.

What blood tests check for tiredness?

That's a decision for your GP, but the common ones for unexplained fatigue include a full blood count, iron studies, thyroid function, vitamin D, vitamin B12 and folate, and blood sugar (HbA1c). Iron deficiency, vitamin D deficiency and an underactive thyroid are three of the most common treatable causes found. Your GP will decide what to test based on your symptoms.

When should I see a doctor about being tired all the time?

See your GP if tiredness has lasted more than two to four weeks, has no obvious explanation, is affecting your daily life, or comes with other symptoms such as breathlessness, weight changes, low mood or feeling faint. Persistent unexplained fatigue is one of the most common reasons people see their GP, and in most cases a cause — often a treatable one — can be found.

Can my mattress really make me tired?

Indirectly, yes. A sagging, too-firm or simply wrong mattress causes you to shift and surface through the night without fully waking, fragmenting your sleep and leaving you tired despite a full night in bed. It won't be the cause of medical fatigue, but it's a cheap, low-risk thing to rule out alongside the other steps here.

Why Am I Always Tired?

Dragging yourself through the day, never quite refreshed no matter how long you were in bed? Constant tiredness is one of the most common complaints there is — and it usually comes down to one of two things: the quality of your sleep, or a physical cause that has nothing to do with sleep at all. Here's how to tell them apart, what to do about each, and when it's time to see your GP.

Written by Seán — Lead Reviewer, MattressReviews.ie

Testing team: Aoife (Side Sleeper Specialist), Ciarán (Back Sleeper Specialist), Siobhán (Combination Sleeper Specialist) & Oisín (Stomach Sleeper Specialist)

3+ years testing mattresses for Irish consumers. How we test · Meet the team

A note on health advice: This guide is for general information only and is not medical advice. Sleep problems can have many causes. If poor sleep is affecting your daily life, lasts more than a few weeks, or you suspect a condition such as insomnia or sleep apnoea, speak to your GP. In Ireland you can also find guidance at HSE.ie.

Start with your sleep quality

The most common reason people feel tired all the time is simply poor-quality or insufficient sleep — and the good news is that this is the most fixable. Hours in bed aren't the same as restorative sleep. Run through these before anything else:

Not enough sleep, or at the wrong times

Most adults need 7–9 hours. An irregular schedule — different bed and wake times each day — also leaves you tired even if the total adds up. See how much sleep you need by age and use our sleep calculator to build a steady routine.

Undiagnosed sleep apnoea

If you snore loudly, gasp or stop breathing in your sleep and wake unrefreshed, sleep apnoea could be fragmenting your nights without you realising. It's very common and very treatable — see our sleep apnoea guide and talk to your GP.

Your bedroom environment

A room that's too warm, too bright or too noisy keeps surfacing you out of deep sleep. A cool, dark, quiet room makes a real difference — our bedroom temperature guide covers the basics.

Caffeine, alcohol & screens

Afternoon caffeine, a nightcap, or scrolling in bed all degrade sleep quality. Alcohol in particular fragments the second half of the night and steals restorative REM sleep.

An old or unsuitable mattress

A sagging or wrong-for-you bed makes you shift and surface all night without fully waking. If you wake stiff, sore or hot, the bed may be part of the problem.

When it's not about sleep: causes to discuss with your GP

If your sleep is genuinely good and you're still exhausted, the cause may be physical. These are common, measurable and usually treatable — but they need a doctor, not guesswork. Bring them up with your GP, who can arrange the right tests.

Iron deficiency

One of the most common causes of fatigue, especially in women who menstruate, in pregnancy, and in people who eat little or no red meat. Low iron means less oxygen reaches your muscles and brain, causing tiredness, breathlessness, pallor and poor concentration. A simple blood test checks for it.

Vitamin D deficiency — a real Irish issue

At Ireland's latitude the sun is too weak from roughly October to March for your skin to make vitamin D — a "vitamin D winter" — and around half of Irish adults are deficient in wintertime. Low vitamin D is linked to fatigue and low mood. The HSE recommends most adults take a 15 microgram vitamin D supplement daily; if you're persistently tired, it's worth raising with your GP or pharmacist.

Thyroid problems

An underactive thyroid (and sometimes an overactive one) disrupts your metabolism and is a classic cause of persistent tiredness, often alongside weight changes, feeling cold, or low mood. A thyroid function blood test checks for it.

Stress, anxiety & low mood

Mental health and tiredness are tightly linked — stress and anxiety disrupt sleep and drain energy, and persistent low mood often shows up as fatigue. Our guides to sleep & anxiety and insomnia in Ireland may help, and your GP can support you with this too.

Other causes worth knowing

Vitamin B12 or folate deficiency, undiagnosed diabetes or other blood-sugar issues, coeliac disease, certain medications, dehydration, and ongoing infections can all cause fatigue. This isn't a list to diagnose yourself from — it's a reminder of why a GP visit and the right blood tests matter when tiredness won't shift.

When to see your GP and get bloods done

"Tired all the time" is one of the most common reasons people visit their GP — you won't be wasting anyone's time. See your GP if your tiredness:

•Has lasted more than two to four weeks without an obvious cause
•Is affecting your work, relationships or daily life
•Comes with other symptoms — breathlessness, unexplained weight change, feeling faint, low mood, or heavy periods
•Doesn't improve even when your sleep and habits are good

Your GP will decide which tests are appropriate, but blood tests for unexplained fatigue commonly include a full blood count, iron studies, thyroid function, vitamin D, B12 and folate, and blood sugar. The point isn't to alarm you — most causes are common and treatable, and a test is the fastest route to feeling like yourself again.

A self-audit checklist

Run through these before your GP visit — it'll make the conversation far more useful. This isn't a diagnosis or a score; it's a prompt to spot the easy fixes and gather the information your doctor needs.

Sleep & habits

Am I getting 7–9 hours most nights?
Are my bed and wake times roughly consistent?
Is my bedroom cool, dark and quiet?
Do I snore loudly or wake gasping?
Am I having caffeine after mid-afternoon, or alcohol at night?
Is my mattress old, sagging or uncomfortable?

Flags to mention to your GP

Tiredness lasting more than 2–4 weeks
Breathlessness, pallor or feeling faint
Heavy periods or a low-iron diet
Unexplained weight change or feeling cold
Low mood, stress or anxiety
Am I taking a daily vitamin D supplement?

Think the bed might be the problem?

If your sleep is broken and the basics are covered, the mattress is worth ruling out. Our 2-minute quiz matches you to the right type and firmness for how you sleep — no email required.

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Frequently Asked Questions

Keep reading

→ Insomnia in Ireland — if you can't fall or stay asleep.
→ Sleep apnoea in Ireland — a common hidden cause of daytime tiredness.
→ Bedroom temperature for better sleep — an easy quality win.
→ Sleep calculator — build a consistent routine.

Sources

HSE — Vitamin D (Irish supplement recommendations). View source
HSE — Iron deficiency anaemia. View source
NHS — Tiredness and fatigue: self-help and when to see a GP. View source