If you are always tired, the most common reasons are everyday ones: not enough or poor-quality sleep, stress, low mood, an unhealthy diet, too little physical activity, too much caffeine or alcohol, and life demands such as caring for a new baby. Hormonal changes and recent illnesses, such as a viral infection, can also leave you drained. When tiredness lasts for weeks without a clear reason, it can point to a medical condition such as iron-deficiency anaemia, an underactive or overactive thyroid, diabetes, sleep apnoea, vitamin B12 deficiency or depression. These are easy to check with a GP visit and simple blood tests.
This guide helps you work through the likely causes, offers practical ways to restore your energy, and lists the signs that mean you should see a doctor.
Tiredness or fatigue: what is the difference?
Everyone feels tired sometimes, after a late night, a hard week or a long journey. That kind of tiredness gets better with rest. Fatigue is different. The NHS describes it as an overwhelming tiredness that isn't relieved by rest and sleep. Unexplained tiredness is one of the most common reasons people see a doctor, so you are not alone. It is also worth taking seriously if it is affecting your daily life.
Common everyday causes of feeling tired all the time
The NHS lists these as the most common causes:
- Not getting enough sleep or finding it hard to fall asleep (insomnia).
- An unhealthy lifestyle, such as a poor diet and little exercise.
- Stress, depression and life challenges, such as bereavement or looking after a new baby.
- Hormonal changes, for example during puberty, pregnancy or the menopause.
- Some illnesses, such as glandular fever and COVID-19, which can leave you tired for a while afterwards.
- Some medicines and treatments, such as chemotherapy, which can cause drowsiness.
Sleep: the first thing to check
Ask yourself honestly how much sleep you get. The NHS suggests aiming for 6 to 9 hours and keeping the same sleep times every day. Late-night screens, irregular shifts, a noisy or hot bedroom and caffeine late in the day all chip away at sleep quality. Our series on how much sleep you really need goes deeper.
Caffeine and alcohol
Caffeine makes you feel more alert at first, but the NHS notes that its effects can last up to 7 hours and can disrupt sleep, leading to more daytime tiredness. It is found in coffee, tea, fizzy drinks, energy drinks and some painkillers. Alcohol may help you fall asleep, but you sleep less deeply afterwards, so you wake up less refreshed. If you want to cut down on caffeine, do it gradually. Stopping suddenly can cause headaches and trouble sleeping.
Food, water and activity
Long gaps between meals, skipped breakfasts and heavy, sugary snacks can leave energy levels swinging. Mild dehydration can also make you feel tired, especially in hot weather (the NHS notes that a glass of water can sometimes do the trick). Being inactive is another surprisingly common cause. Exercise feels like the last thing you want to do when you are tired, but the NHS says regular activity makes you feel less tired in the long run.
Medical causes of constant tiredness
If your tiredness has gone on for a while, isn't improving and you can't explain it, a health condition may be the reason. The NHS lists these clues:
| Other symptoms alongside tiredness | Possible cause |
|---|---|
| Waking at night, loud snoring, gasping, snorting or choking noises during sleep, daytime sleepiness | Sleep apnoea |
| Lack of energy, noticeable heartbeats (palpitations), shortness of breath, pale skin | Iron-deficiency anaemia |
| Feeling very thirsty, peeing more often (especially at night), weight loss | Diabetes |
| Restlessness, nervousness, anxiety, irritability, muscle weakness | Overactive thyroid (hyperthyroidism) |
| Extreme fatigue for at least 3 months that makes daily life very hard, problems with memory and concentration, flu-like symptoms | ME/CFS (myalgic encephalomyelitis / chronic fatigue syndrome) |
Other conditions that commonly cause tiredness include:
- Underactive thyroid (hypothyroidism). It often comes with weight gain, feeling cold, constipation and dry skin. See our guide to hypothyroidism symptoms and thyroid tests.
- Vitamin B12 or folate deficiency. This is more likely in people who eat little or no animal food, older adults and people on certain long-term medicines. Read more in our vitamin B12 explainer.
- Depression and anxiety. Low mood, loss of interest and poor sleep often go hand in hand with exhaustion.
- Long-term conditions such as kidney or liver disease, heart problems or coeliac disease. These are less common causes, and your doctor will look for other clues.
Iron-deficiency anaemia deserves special mention because it is common, particularly among women with heavy periods, during pregnancy, and in people whose diet is low in iron. A simple blood count and iron studies can confirm it. Our guide to iron studies and ferritin explains the results. Don't start iron supplements without a test, because too much iron can be harmful.
Practical ways to boost your energy
For many people, these steps from the NHS make a real difference within a few weeks.
Sleep habits
- Go to bed and get up at the same time every day, including weekends.
- Aim for 6 to 9 hours, and avoid long daytime naps.
- Relax for a couple of hours before bed, for example by reading or listening to music.
- Keep the bedroom dark, quiet and not too warm.
- Avoid screens for the last hour before bed, and avoid eating, caffeine and exercise in the couple of hours before.
Food and drink
- Eat regular meals and healthy snacks every 3 to 4 hours rather than one or two very large meals.
- Build meals around whole grains, pulses, vegetables, fruit and some protein. Include iron-rich foods such as dals, leafy greens, eggs, fish or meat, with vitamin C-rich foods to help absorption.
- Drink enough water through the day.
- Cut down on caffeine, especially after lunch, and keep alcohol within low-risk limits. The NHS advises no more than 14 units a week, with several alcohol-free days.
Movement and stress
- Start small. The NHS notes that even a single 15-minute walk can give you an energy boost. Build up gradually towards 150 minutes of moderate activity a week.
- Lose excess weight if you need to. Carrying extra weight can be tiring and strains the heart.
- Make time to relax, whether through yoga, music, reading or time with friends. Even short daily breaks help.
- Consider talking therapy. The NHS says there is some evidence that counselling or cognitive behavioural therapy (CBT) can help with tiredness caused by stress, anxiety or low mood.
When to see a doctor about tiredness
The NHS advises seeing a GP if:
- you've been feeling tired for a few weeks and don't know why
- your tiredness is affecting your daily life
- you have other symptoms, such as weight loss or changes in mood, or someone has told you that you gasp, snort or choke while asleep
Get help urgently if tiredness comes with chest pain, severe breathlessness, fainting, blood in your stool or vomit, or thoughts of harming yourself.
What the doctor may check
A doctor will ask about your sleep, mood, diet, periods, medicines, alcohol and caffeine, and any other symptoms. Treatment depends on the cause. According to the NHS, you may need blood tests to check for anaemia, diabetes or thyroid problems. Doctors often also check vitamin B12, kidney and liver function. Treatment may include advice on sleep and lifestyle, talking therapies such as CBT, or treatment for any condition that is found. If no cause is clear, you may be referred to a specialist.
Frequently asked questions
Why am I tired even after 8 hours of sleep?
Sleep quality matters as much as the hours. Sleep apnoea, alcohol, late caffeine, stress and a disturbed sleep environment can all leave you unrefreshed. Anaemia, thyroid problems or low mood can also cause tiredness despite enough sleep. If it persists, see a doctor. Our piece on snoring and sleep apnoea explains the warning signs.
Which vitamin deficiency causes tiredness?
Iron deficiency (anaemia) and vitamin B12 or folate deficiency are well-known causes. Low vitamin D is often blamed too, but evidence that it causes tiredness is less clear. A blood test is the only way to know. Taking supplements without testing is not recommended.
Can stress make you physically tired?
Yes. The NHS notes that stress uses up a lot of energy, and it often disrupts sleep too. Managing stress and getting help for anxiety or low mood can improve energy levels.
Are energy drinks a good fix?
They give a short-term boost from caffeine and sugar, but they can disrupt sleep and make tiredness worse over time. Water, regular meals, activity and better sleep are more reliable.
What blood tests check for tiredness?
Doctors commonly order a full blood count, iron studies and ferritin, thyroid function, blood sugar or HbA1c, and often vitamin B12, kidney and liver tests. The exact tests depend on your symptoms.
Disclaimer: This article is for general information only and is not medical advice. It does not replace a diagnosis or treatment plan from a qualified professional. Please consult your doctor before changing your diet, exercise, medicines or supplements, and seek urgent care for any warning signs mentioned above.
Related reading on HorizonDesk
- Hypothyroidism: symptoms, thyroid tests and diet tips
- Lab tests explained: iron studies, ferritin and anaemia
- Vitamins and minerals explained: vitamin B12
- Sleep science: snoring and sleep apnoea
- Sleep science: how much sleep you need
