Fatigue: Why You Feel Tired All the Time

Fatigue vs tiredness vs sleepiness

• Tiredness is normal after effort and goes away with rest or sleep.
• Fatigue is persistent exhaustion that rest does not fix. It may be physical (heavy limbs, weakness) or mental (poor concentration, brain fog).
• Sleepiness is a strong urge to fall asleep, often at inappropriate times. It points to sleep disorders such as sleep apnea or narcolepsy.
• Weakness is a loss of muscle power, which suggests nerve or muscle disease rather than fatigue.

Telling these apart helps a doctor narrow the cause.

Common causes of constant tiredness

Lifestyle and sleep

• Not enough sleep: adults need 7 to 9 hours. Shift work, young children and late-night screen use cut into it.
• Poor quality sleep: from insomnia, noise, pain, caffeine late in the day, or alcohol, which fragments sleep.
• Inactivity: paradoxically, being inactive increases fatigue.
• Diet: skipping meals, very low-calorie diets and too much sugar cause energy swings.
• Overwork and stress.

Mental health

Depression commonly presents as fatigue, with low mood, loss of interest, poor sleep and poor concentration. Anxiety, grief and burnout also drain energy.

After infections

Tiredness can last weeks after flu, COVID-19 or glandular fever. Long COVID and post-viral fatigue can last months.

Medicines and substances

Antihistamines, some blood pressure medicines (beta-blockers), antidepressants, sleeping pills, opioids, anti-seizure medicines and chemotherapy commonly cause fatigue. Alcohol, cannabis and caffeine withdrawal do too.

Medical causes of fatigue

Chronic fatigue syndrome (ME/CFS)

Chronic fatigue syndrome, or myalgic encephalomyelitis, is diagnosed when profound fatigue lasts 6 months or more, with:

• post-exertional malaise: symptoms worsen for a day or more after even minor effort
• unrefreshing sleep
• problems with thinking and memory, or feeling worse when standing upright

It is diagnosed after other causes have been excluded. Pacing activity within your energy limits is central to management.

When to worry about fatigue

See a doctor if fatigue:

• lasts more than 4 weeks without explanation
• comes with unexplained weight loss, fever, night sweats or swollen glands
• comes with breathlessness, chest pain or palpitations
• comes with bleeding, black stools or very heavy periods
• stops you working, studying or looking after yourself

How doctors assess fatigue

Your doctor will ask how long you have felt tired, about sleep, snoring, mood, stress, diet, alcohol, medicines, periods and pregnancy, and other symptoms. A physical examination checks for pallor, thyroid swelling, lymph nodes, heart and lung signs, and fluid retention.

Initial blood tests usually include:

• complete blood count and ferritin (iron stores)
• thyroid function (TSH)
• blood sugar or HbA1c
• kidney and liver function
• inflammatory markers (CRP or ESR)
• celiac screen, vitamin B12 and vitamin D in some cases

A sleep study is arranged if sleep apnea is suspected. Most people with fatigue have normal tests, and lifestyle or mood factors explain their symptoms.

Treatment and self-help

Treatment depends on the cause: iron, thyroid hormone, B12 replacement, diabetes treatment, CPAP for sleep apnea, or treatment for depression. Alongside this:

• Keep regular sleep hours, including weekends, and aim for 7 to 9 hours.
• Cut caffeine after noon and limit alcohol.
• Move more: gradual, regular activity, such as a daily walk, improves energy within weeks for most people. People with ME/CFS should pace activity instead.
• Eat regularly, with protein and whole grains for steady energy.
• Manage stress: realistic workloads, breaks, and talking therapies if needed.
• Review medicines with your doctor or pharmacist.

Frequently asked questions

Why am I tired all the time?

The most common reasons are not enough or poor-quality sleep, stress, low mood, alcohol and inactivity. Medical causes such as anemia, an underactive thyroid, diabetes and sleep apnea are also common. If tiredness lasts more than 4 weeks, ask your doctor for an assessment and blood tests.

What blood tests check for fatigue?

Doctors usually check a complete blood count, ferritin (iron stores), thyroid function, blood sugar or HbA1c, kidney and liver function, and inflammatory markers. Vitamin B12, vitamin D and celiac tests are added depending on symptoms.

Can fatigue be a sign of something serious?

Usually it is not, but it can be an early sign of anemia, diabetes, heart failure, kidney disease or cancer. Fatigue with weight loss, night sweats, fever, bleeding or breathlessness needs prompt medical attention.

What is extreme fatigue a symptom of?

Extreme fatigue can result from severe anemia, uncontrolled diabetes, heart failure, major depression, chronic fatigue syndrome, cancer and its treatment, or recovery from serious infections such as COVID-19 or glandular fever.

What vitamin deficiency causes fatigue?

Iron deficiency is the most common, followed by vitamin B12 and folate deficiency. Low vitamin D can cause tiredness and muscle aches. Blood tests confirm a deficiency before supplements are started.