Why Am I Always Tired? 8 Causes Worth Ruling Out

Sleeping eight hours and waking up unrefreshed is a specific complaint, and a common one. It is also one of the few symptoms where the obvious fix — more sleep — frequently does nothing, because the problem is rarely the quantity of sleep.

Persistent fatigue lasting more than two or three weeks is worth investigating properly. Below are the causes clinicians look for first, roughly in order of how often they turn out to be the answer.

1. Sleep that is broken rather than short

You can spend eight hours in bed and get very little restorative sleep. Obstructive sleep apnoea is the classic example: breathing repeatedly pauses, oxygen dips, and the brain surfaces briefly hundreds of times a night without you ever remembering waking. The tell-tale signs are loud snoring, gasping, a partner who has noticed you stop breathing, morning headaches, and daytime sleepiness severe enough to make driving unsafe.

Sleep apnoea is common, badly underdiagnosed, and treatable. If any of that sounds familiar, it belongs at the top of your list.

2. Iron deficiency

One of the most frequent reversible causes, especially in menstruating women, vegetarians, frequent blood donors, and anyone with heavy periods or gut bleeding. Fatigue often arrives well before anaemia is visible, alongside breathlessness on stairs, pale skin, brittle nails, or unusual cravings for ice.

A ferritin test alongside a full blood count is what identifies it. Do not start iron supplements on your own — excess iron accumulates and causes its own harm, and self-supplementing can mask bleeding that needed to be found.

3. Thyroid function

An underactive thyroid slows everything down: fatigue, weight gain, feeling cold, dry skin, constipation, low mood, heavier periods. It is diagnosed with a simple blood test (TSH, usually with free T4) and treated with daily replacement. An overactive thyroid can also cause exhaustion, but through restlessness and poor sleep rather than sluggishness.

4. Vitamin B12 and vitamin D

B12 deficiency causes fatigue with pins and needles, a sore tongue, and sometimes memory or balance problems. It is more common in people over 60, vegans, anyone taking metformin or long-term acid-reducing drugs, and people who have had gastric surgery. Low vitamin D is widespread and associated with fatigue and muscle aches, particularly where sun exposure is limited.

5. Depression and anxiety

Fatigue is one of the most reliable physical signs of depression, and it often shows up before low mood is recognised as such — as loss of interest, difficulty concentrating, and waking at 4am unable to get back to sleep. This is not "fatigue with no physical cause." The exhaustion is real and it responds to treatment.

6. Blood sugar

Both undiagnosed diabetes and reactive blood sugar swings cause tiredness. Increased thirst, frequent urination, unexplained weight loss, and blurred vision alongside fatigue warrant a blood glucose or HbA1c test promptly.

7. Medication side effects

Antihistamines, beta blockers, some antidepressants, sedatives, and blood pressure medications all list fatigue. So does the combination of several drugs that are individually fine. Bring a complete list — prescriptions, over-the-counter, supplements — to your appointment. This cause is easy to find and easy to fix, and it is missed constantly.

8. The everyday drivers

Dehydration, caffeine late in the day, alcohol before bed (it induces sleep and then fragments it), a stimulating screen at midnight, an inconsistent wake time, and long stretches without movement all degrade sleep quality. These are worth correcting for two weeks — both because they may be the answer, and because correcting them makes any remaining fatigue much easier to interpret.

See a doctor sooner rather than later if

• Fatigue is severe or has lasted more than two to three weeks despite decent sleep
• It comes with unexplained weight loss, fever, night sweats, or swollen glands
• You are breathless at rest or on mild exertion
• You have chest pain or palpitations
• Someone has observed you stop breathing in your sleep
• You feel hopeless or unsafe

What a useful appointment looks like

Track two weeks before you go: bedtime and wake time, how rested you feel out of ten, caffeine and alcohol, and anything that reliably makes it worse. Fatigue is a vague complaint until it has a pattern attached, and the pattern is the part only you can supply.

Expect blood tests. A reasonable first panel usually covers full blood count, ferritin, thyroid function, B12, vitamin D, blood glucose or HbA1c, and kidney and liver function — enough to catch most of the list above in one draw.