Always Tired? Common Causes and Which Blood Tests Help

Feeling always tired usually has a cause that can be found. Common ones are poor sleep, stress, anxiety or low mood, anaemia, thyroid problems, diabetes or a medicine. If it lasts more than a few weeks with no clear reason, see a doctor and get a basic blood test. This guide is by Dr. Pedro Yelamo Vera, a GP licensed in Spain (Colegiado No. 484814280).

Why am I always tired?

Most often it is a mix of daily life and, sometimes, a health problem. Tiredness is not an illness. It is a symptom. So a doctor first asks how you sleep, eat and work, how your mood is and which medicines you take. Then they decide on tests.

What are the most common causes of tiredness?

• Sleep: too little sleep, insomnia, shift work, or sleep apnoea (loud snoring and pauses in breathing).
• Stress, anxiety and depression: some of the most common causes. Tiredness may be the first sign.
• Anaemia and low iron: mostly with heavy periods, in pregnancy, or with diets low in iron.
• Underactive thyroid: tiredness, feeling cold, constipation and weight gain.
• Diabetes: with thirst and passing a lot of urine.
• Recent infections: after flu or COVID-19, tiredness can last for weeks.
• Medicines, alcohol and caffeine: some antihistamines, antidepressants and blood pressure medicines make you tired.
• Pregnancy, mostly in the first months.

Less often, tiredness comes from heart, kidney or liver disease, coeliac disease or chronic fatigue syndrome (ME/CFS).

Which blood tests should I ask for if I am always tired?

There is no single test for tiredness. The doctor picks tests to fit your case. The most useful are often:

• a full blood count, to check for anaemia;
• ferritin, which shows your iron stores;
• TSH, for the thyroid;
• blood sugar or HbA1c, for diabetes;
• kidney and liver tests, and salts such as sodium, potassium and calcium;
• if needed, vitamin B12, folate, vitamin D, CRP or a coeliac test.

In Spain, ask for hemograma, ferritina, TSH and glucosa. Normal results do not mean the tiredness is in your head. Often the cause is sleep or mood.

Why am I tired with weak legs?

Heavy or weak legs with tiredness are often due to lack of exercise, anaemia or poor sleep. Other causes include low potassium, low vitamin B12 or vitamin D, some medicines (such as statins or water tablets), or problems with blood flow or nerves. See a doctor if the weakness gets worse, if stairs or getting out of a chair get hard, or if you have tingling. Sudden weakness on one side of the body is an emergency.

When is it normal to feel tired?

It is normal after a few weeks of hard work, short nights or an infection, and it gets better with rest. It is not normal if it lasts more than a month, does not get better with sleep, or stops you living your life.

What can I do at home?

• Go to bed and get up at the same time, weekends too.
• Move every day. A 30-minute walk helps more than resting on the sofa.
• Eat at regular times and drink water.
• Cut down on alcohol, and avoid caffeine after lunch.
• Do not start iron or vitamin pills without a blood test. They may hide a cause or not be needed.

When to see a doctor soon

• Tiredness lasts more than 4 weeks with no clear cause.
• You lose weight without trying, or have a fever or night sweats.
• You get short of breath, have palpitations, or feel faint when you stand.
• You have very heavy periods, black stools or blood in your stools.
• You snore loudly and fall asleep in the day.
• You feel low or lose interest in things most of the day. A depression test can help you put it into words.

When to call 112

• Sudden weakness or numbness of the face, an arm or a leg, mostly on one side.
• Sudden trouble speaking or seeing.
• Chest pain or severe shortness of breath.
• Leg weakness that spreads up over hours or days and stops you walking.

If you have thoughts of suicide, call 024, Spain's free suicide prevention line, or 112 if you are in danger now.

Frequently asked questions about tiredness

Getting a medical assessment

If you have felt tired for weeks and want to know why, you can book a video consultation with Dr. Pedro Yelamo Vera, a physician registered in Spain. You can also read about blood test reviews. A prescription is never guaranteed: it is issued only where clinically appropriate after a genuine evaluation, as a private electronic prescription under Spanish law. This service is for urgent, non-emergency care. In an emergency, call 112.

This guide is general information. It does not replace the package leaflet or the advice of your doctor or pharmacist.