Why Am I Tired All the Time? 8 Medical Causes Worth Checking
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Most of us use "tired" and "fatigued" interchangeably. Clinically, they're different.
Tiredness is what you feel after a busy week, a poor night's sleep, or a hard workout. It improves with rest.
Fatigue is the heavier, more persistent version. It doesn't lift after a weekend off. It can include trouble concentrating, low motivation, and feeling like simple tasks take more effort than they should. When fatigue lasts more than a few weeks, it's worth checking what might be driving it — it's one of the most common reasons Australians see a GP, and there's almost always something useful to learn.
The other reason the distinction matters: persistent fatigue is one of the few symptoms that touches almost every body system. Iron stores, thyroid function, blood sugar, sleep quality, mood, hormones, infection, inflammation — any of them, in the wrong range, can leave you running on empty. That's why a careful history and a few targeted tests usually reveal the cause.
Iron deficiency is one of the most common reversible causes of tiredness in Australia, particularly in menstruating women, vegetarians and vegans, and people with heavy periods, pregnancy, or gut absorption issues.
Symptoms beyond tiredness: pale skin, breathlessness on stairs, brittle nails, restless legs at night, hair shedding, headaches, and feeling cold easily.
A simple blood test (full blood count and iron studies) can confirm whether iron is the issue. Treatment depends on the cause and severity — your GP will guide you, and severe cases sometimes need iron infusions rather than tablets.
Your thyroid is a small gland in your neck that sets the pace for your metabolism. When it's underactive (hypothyroidism), everything slows down — energy, mood, digestion, and temperature regulation.
Symptoms beyond tiredness: weight gain that's hard to shift, feeling cold, dry skin, brain fog, constipation, low mood, hair thinning, and slow pulse.
Thyroid disease is more common in women, particularly after pregnancy and around perimenopause. A blood test (TSH, sometimes T4 and antibodies) is the starting point. Treatment is well-established and typically very effective once started.
You can spend nine hours in bed and still wake up exhausted if your sleep quality is poor.
The big drivers:
- Sleep apnoea — breathing repeatedly pauses during the night. Often missed because the person snoring rarely notices it. Partners do. Daytime sleepiness, morning headache, and witnessed pauses in breathing are red flags.
- Insomnia — trouble falling or staying asleep, or waking too early.
- Restless legs syndrome — uncomfortable sensations in the legs at night that disrupt sleep.
- Shift work — your body never fully resets to one sleep window, and the cumulative debt builds.
If you're hitting your hours but still tired, sleep quality is worth investigating. For more on what your body actually needs, see How Much Sleep Do Adults Actually Need. For options when sleep won't come, see Sleep Medication in Australia: What a GP Can Prescribe.
Persistent low energy is one of the core features of depression, even when sadness isn't the most obvious symptom. Many people describe it as "I'm just flat" or "I can't be bothered with anything anymore."
Anxiety can also exhaust you — your body has been on high alert for weeks. Burnout (a specific syndrome of emotional exhaustion, cynicism, and reduced effectiveness, usually work-driven) is increasingly recognised as a distinct contributor.
Mental health and physical health are not separate boxes. A good GP will ask about both. There's no blood test for depression or burnout, but there are validated questionnaires and lots of options for support — talking therapies, lifestyle changes, structured time off, and sometimes medication.
Need time off work?
5. Vitamin D and B12 deficiency. Both are common in Australia despite the sunshine. Tiredness, low mood, muscle aches, and tingling in the hands or feet are typical signs. Easy to test, easy to correct.
6. Diabetes and blood-sugar issues. Constant tiredness, increased thirst, frequent urination, and unexplained weight changes can all point to a problem with blood sugar regulation. Pre-diabetes and type 2 diabetes are increasingly common in Australia and worth screening for, especially after age 40 or with a family history.
7. Chronic infections and post-viral fatigue. Some viruses (including influenza, COVID-19, glandular fever) can leave fatigue lingering for weeks or months. Long COVID is a recognised cause of persistent post-infection fatigue.
8. Medication side effects. Beta-blockers, antihistamines, certain antidepressants, blood pressure medications, and sleeping pills can all cause daytime tiredness. If your fatigue started after a medication change, that's worth flagging to your GP.
There are other less common causes — coeliac disease, kidney or liver problems, hormonal conditions, and chronic fatigue syndrome (myalgic encephalomyelitis). They're less common but real, and a careful workup looks for them too.
Book a consult if:
- You've been tired most days for more than 2–4 weeks without an obvious reason
- You're sleeping enough hours but still waking unrefreshed
- The fatigue is affecting your work, relationships, or daily function
- You have other symptoms — weight change, mood change, breathlessness, periods that have changed, pain, fevers, or something just feels off
Urgent — see a doctor sooner if:
- Sudden severe fatigue with shortness of breath or chest pain
- Fatigue with confusion, fainting, or unable to keep fluids down
- Fatigue with bleeding (heavy periods, blood in stool or urine)
- Significant unintentional weight loss
Abby Health is an online-first Australian clinic. Our GPs are AHPRA-registered. When you book a consult, Abby AI, our medical AI, prepares a clinical brief for your doctor — including your symptoms, medical history, medications, and how long the tiredness has been going on — so they're already informed when you connect.
For persistent tiredness, your Abby GP can take a thorough history, order the right blood tests through your local pathology collection centre, review the results with you, and either treat the cause directly (iron, thyroid, vitamin D, mental health support) or refer you on to a specialist or sleep service if needed. If you're an Abby patient who already has a regular doctor at the clinic, your history is already there — you don't have to start from scratch.
For more on sleep itself, see How Much Sleep Do Adults Actually Need. If a script is needed and you'd rather not return for a paper one, see How to Refill a Prescription Online. If you need time off work while you investigate, see how to get an online medical certificate in Australia.
Abby Health consultations are bulk billed for eligible patients with a valid Medicare card.
Find Comfort. Abby Health. Care that understands you.
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