Everyone feels tired sometimes. But if you feel drained for weeks even after a full night in bed, it is worth looking for a reason. This guide covers the most common causes of low energy, which ones need a doctor’s attention, and what you can try yourself.
Quick answer
- Sleep problems, stress and low mood are among the most common causes of ongoing tiredness.
- Medical causes include iron deficiency anemia, vitamin B12 or folate deficiency, thyroid problems, diabetes and sleep apnea.
- See a doctor if you have been tired for a few weeks and do not know why, or if tiredness comes with other symptoms such as weight loss.
Normal tiredness vs. persistent fatigue
Feeling tired after a bad night, a busy week or hard exercise is normal and usually passes with rest. Persistent fatigue is different: it lasts for weeks, affects your daily life, and does not improve much with sleep. That pattern is a reason to get checked.
Common causes of low energy
1. Poor or not enough sleep
Not getting enough sleep, or getting poor-quality sleep, is the most obvious cause. If you often wake at night, see our guide on why you might wake up at 3AM.
2. Stress, anxiety and low mood
Sleep disorders, depression and high stress are described as the most common causes of persistent fatigue. Mental load can be as draining as physical effort. Feeling flat, hopeless or losing interest in things alongside tiredness is a reason to talk to a doctor.
3. Sleep apnea
In sleep apnea, breathing repeatedly pauses during sleep. You may not remember it, but you wake up unrefreshed. Loud snoring, gasping at night and daytime sleepiness are warning signs.
4. Iron deficiency anemia
Anemia means the blood carries less oxygen. Symptoms can include tiredness and lack of energy, shortness of breath, noticeable heartbeats, paler skin and headaches. It is often caused by blood loss (for example heavy periods) or a diet low in iron, and it is confirmed with a blood test. Do not start iron supplements without testing, because the cause needs to be found.
5. Low vitamin B12 or folate
Low B12 can cause fatigue and, in some people, nerve symptoms such as tingling. Causes include poor absorption (for example pernicious anemia), stomach or bowel surgery, long-term use of some medicines such as metformin or acid-reducing drugs, and diets with no animal foods unless supplemented.
6. Thyroid problems
Thyroid disorders can cause tiredness, and an overactive thyroid is listed by the NHS as one cause. A simple blood test can check thyroid function.
7. Diabetes
High blood sugar can make you feel very tired. Other signs include being very thirsty, passing urine more often and unexplained weight loss.
8. Medicines, alcohol and infections
Some medicines list tiredness as a side effect. Alcohol and late caffeine can also disrupt sleep. Infections such as glandular fever and COVID-19 can leave you tired for weeks, and ME/CFS is a long-term condition that a doctor must diagnose.
What you can try yourself
- Keep a regular sleep and wake time.
- Do some physical activity most days. Even a 15-minute walk can give an energy boost.
- Get outside in the morning light.
- Eat regular balanced meals and drink enough fluids.
- Limit alcohol and keep caffeine to the earlier part of the day.
For a fuller list, read 10 ways to boost your energy naturally. If tiredness comes with strong mood swings, see why you feel emotional when you are tired.
When to see a doctor
- You have felt tired for a few weeks and do not know why.
- Tiredness is affecting your daily life or work.
- You also have unexplained weight loss, mood changes, shortness of breath, or a racing heartbeat.
- It is getting worse rather than better.
A doctor may ask about your sleep, mood and medicines, and may order blood tests to check for anemia, diabetes and thyroid problems.
Frequently asked questions
Why am I tired all the time even though I sleep 8 hours?
Sleep quality matters as much as length. Sleep apnea, stress, low mood, anemia, thyroid problems and some medicines can all cause tiredness despite enough hours in bed.
Can supplements fix low energy?
Only if you are actually deficient in something. Ask for tests first, because the wrong supplement will not help and some can cause harm.
How long is too long to feel tired?
If it lasts more than a few weeks without a clear reason, book an appointment.
Sources
- Tiredness and fatigue — NHS
- Iron deficiency anaemia — NHS
- Vitamin B12 deficiency anemia — MedlinePlus
- Fatigue as the Chief Complaint: Epidemiology, Causes, Diagnosis, and Treatment — PMC
- Self-help tips to fight tiredness — NHS
Medical disclaimer: This article is for general information only and is not medical advice. It may contain inaccuracies or may not apply to your situation. Please talk with a doctor or pharmacist before making decisions about supplements, medicines or treatment.