Why Am I Always Tired?

Intro

Tiredness is one of the most common reasons people visit a doctor. Feeling chronically fatigued — dragging through the day, waking unrefreshed, struggling to concentrate — is never normal when it persists. It is always a signal worth investigating, even when no obvious cause is apparent.

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Key Points

Persistent unexplained fatigue should always be investigated — it is not something to simply push through indefinitely.
The most common identifiable causes are poor or insufficient sleep, sleep apnoea, depression, anxiety, iron deficiency anaemia, thyroid disease, and diabetes.
More than one cause is often present simultaneously.
Chronic Fatigue Syndrome / ME is a distinct, specific diagnosis — not the same as general tiredness from common medical causes.
Most causes are diagnosable with a clinical assessment and basic blood tests.

Distinguishing This from CFS/ME

If you have been diagnosed with Chronic Fatigue Syndrome (CFS/ME), see Chronic Fatigue Syndrome for a condition-specific guide. CFS/ME is characterised by severe post-exertional malaise (worsening of symptoms after physical or mental effort), cognitive dysfunction, and orthostatic intolerance. It is distinct from the common causes of fatigue discussed here and requires different assessment and management.

Common Causes

1. Insufficient or Poor-Quality Sleep

The most common cause of daytime tiredness is not getting enough sleep — or not getting restorative sleep. Adults need 7–9 hours. Many people function chronically below this threshold while substantially underestimating the impairment it causes.

Poor sleep quality can result from irregular schedules, late caffeine or alcohol, excessive screen use before bed, a bedroom that is too warm or light, or anxiety that fragments sleep.

See Sleep Health: Why It Matters and How to Improve It and Healthy Sleep Hygiene.

2. Obstructive Sleep Apnoea

Sleep apnoea is one of the most underdiagnosed causes of chronic tiredness. In obstructive sleep apnoea (OSA), the upper airway repeatedly collapses during sleep, causing hundreds of brief arousals per night — none of which reach consciousness, but all of which fragment sleep architecture and prevent restorative sleep.

Signs that suggest sleep apnoea:

Loud snoring
Breathing pauses witnessed by a partner
Gasping or choking during sleep
Waking unrefreshed despite 7–9 hours in bed
Persistent daytime sleepiness that does not improve with more sleep
Morning headaches

OSA is diagnosed with a sleep study and is highly treatable. Most people with OSA experience dramatic improvements in energy and cognition after starting CPAP therapy.

3. Iron Deficiency Anaemia

Iron deficiency is the most common nutritional deficiency globally and a very common cause of fatigue — particularly in women of reproductive age, pregnant women, vegetarians, and people with heavy menstrual bleeding or gastrointestinal blood loss.

Symptoms include fatigue, pallor, breathlessness on exertion, palpitations, difficulty concentrating, cold intolerance, and — in more severe cases — brittle nails or hair loss.

Diagnosed with a full blood count and ferritin level. Treated with oral iron supplementation; the underlying cause should always be identified and addressed.

4. Depression

Depression is one of the most common causes of persistent fatigue. Fatigue and low energy are core symptoms alongside low mood, loss of pleasure, cognitive slowing, and sleep disturbance.

Depression-related fatigue has a characteristic quality: everything feels effortful, motivation is absent, and activity does not relieve tiredness. Sleep disturbance — typically early morning waking — is common. Fatigue and depression are bidirectionally linked: poor sleep worsens depression, and depression worsens sleep.

5. Anxiety

Anxiety disorders — particularly generalised anxiety disorder — produce physical exhaustion through sustained hyperarousal. The body running its threat-response system chronically is metabolically expensive. Disrupted sleep from racing thoughts amplifies the fatigue further.

6. Hypothyroidism

An underactive thyroid gland reduces metabolic rate and causes fatigue, cold intolerance, weight gain, constipation, low mood, cognitive slowing, and dry skin. It is more common in women and older adults.

Diagnosed with a TSH blood test; treated effectively with levothyroxine replacement.

7. Type 2 Diabetes and Prediabetes

Both type 2 diabetes and prediabetes are associated with fatigue — partly from disrupted cellular energy metabolism due to insulin resistance, and partly from associated sleep disruption, frequent nocturia, and, over time, peripheral neuropathy.

8. Vitamin and Mineral Deficiencies

Beyond iron, deficiencies in vitamin B12, vitamin D, and folate can all cause fatigue. Vitamin B12 deficiency is particularly common in older adults, vegans, and people on long-term metformin. Vitamin D deficiency is endemic in northern latitudes and associated with fatigue, low mood, and musculoskeletal symptoms.

9. Medication Side Effects

Many common medications cause fatigue as a side effect:

Beta-blockers (hypertension, heart disease)
Antihistamines
Benzodiazepines and sedative-hypnotics
Many antidepressants (particularly at initiation or dose change)
Statins (in some people)
Opioid analgesics
Anti-epileptic drugs

If fatigue began or worsened after starting a new medication, discuss a dose adjustment or switch with your prescriber.

10. Chronic Medical Conditions

Many chronic conditions cause fatigue as a primary symptom:

Chronic kidney disease — waste product accumulation and anaemia of chronic disease
Heart failure — reduced cardiac output impairs exercise tolerance and causes fatigue even at rest
COPD — hypoxia and sleep disruption
Inflammatory conditions — rheumatoid arthritis, lupus, inflammatory bowel disease
Long COVID and post-viral syndromes — post-viral fatigue affecting energy, cognition, and exertion tolerance. See Post-Viral Syndromes
Restless Legs Syndrome — sleep fragmentation from nocturnal leg discomfort causes significant daytime tiredness

11. Poor Diet, Dehydration, and Inactivity

Erratic eating, skipping meals, and high ultra-processed food intake destabilise blood glucose and contribute to low energy. Mild dehydration consistently impairs energy and concentration. Paradoxically, physical inactivity causes fatigue — regular aerobic exercise is one of the most reliable ways to improve energy levels over time.

When to Seek Medical Advice

See a doctor if:

Fatigue has persisted for more than 4 weeks without an obvious cause
It is significantly affecting work, relationships, or daily functioning
It is accompanied by:
- Unintentional weight loss
- Persistent fever or night sweats
- Shortness of breath on minimal exertion
- Chest pain or palpitations
- Swollen lymph nodes
- Severe or worsening low mood
- Heavy or irregular menstrual bleeding
You suspect sleep apnoea (loud snoring, gasping, witnessed breathing pauses, or excessive daytime sleepiness despite adequate time in bed)
You have a condition that commonly causes fatigue and your fatigue has changed in character or severity

Do not defer investigation on the assumption that it is “probably just stress.” Fatigue is a legitimate medical symptom.

What to Expect at the Appointment

A doctor will typically:

Take a full history — onset, character, associated symptoms, medications, lifestyle
Perform a clinical examination
Order basic blood tests: full blood count, thyroid function, fasting glucose or HbA1c, ferritin, vitamin B12, vitamin D, CRP or ESR, kidney and liver function
Ask about sleep — volume, quality, snoring, partner observations
Screen for depression and anxiety

Most common causes can be identified or strongly suspected from this initial assessment.

FAQ

Q: What are the most common causes of persistent tiredness?
A: Insufficient or poor-quality sleep, sleep apnoea, depression, anxiety, iron deficiency anaemia, hypothyroidism, type 2 diabetes, and medication side effects. Multiple causes often coexist.

Q: When should I see a doctor?
A: If fatigue has lasted more than 4 weeks, is unexplained by obvious factors, is significantly impairing daily function, or is accompanied by other symptoms such as weight change, breathlessness, palpitations, or mood disturbance.

Q: What blood tests are usually done?
A: A standard screen includes full blood count, thyroid function, fasting glucose or HbA1c, ferritin, vitamin B12, vitamin D, CRP or ESR, and kidney and liver function.

Q: Is tiredness always a sign of something serious?
A: Not always. Many causes are common, treatable, and not life-threatening. But persistent fatigue that does not respond to good sleep and lifestyle measures should always be investigated rather than normalised.

Q: Is chronic fatigue syndrome the same as being always tired?
A: No. CFS/ME is a specific diagnosed condition with distinct clinical criteria involving post-exertional malaise, cognitive dysfunction, and autonomic features. See Chronic Fatigue Syndrome.