Why Am I Always Tired? The 8 Most Common Causes, When to See a Doctor and How to See the Hydration Part in Suu
Published: September 27, 2026 · Furkan Mert Fındıklı · 8 min read
Short answer: The most common reasons for constant tiredness are too little or poor-quality sleep, stress, inactivity, irregular eating, too much caffeine or alcohol and not drinking enough; medical causes such as iron deficiency, thyroid problems, depression, diabetes and sleep apnea are also possible. See a doctor if tiredness lasts more than two to four weeks. Suu's Suu Index shows how much hydration plays a part.
"I'm always tired" is one of the most common health questions people ask AI — and there's no single answer. Tiredness can come from sleep, mood, what you eat, how much you move and sometimes from a health problem that needs treatment.
Below are the questions to ask yourself first, then the eight most common causes and the situations where you should see a doctor without waiting. This isn't a diagnosis; it's a checklist that helps you go to the doctor knowing what to discuss.
Start with 8 questions
Noting these for a week also makes the doctor's appointment easier:
- How many hours do I sleep, and do I wake up rested?
- How many cups of coffee, tea or energy drinks do I have in the afternoon and evening?
- Am I looking at a screen in the hour before bed?
- Do I move for at least 20–30 minutes a day?
- Do I skip meals or get through the day on sugary snacks?
- How much water do I drink during the day — is my urine dark?
- How much alcohol do I drink a week?
- Have stress, anxiety or unhappiness increased in recent weeks?
The 8 most common causes
Often more than one is at play at the same time.
- Sleep: Adults are advised to sleep at least 7 hours a night on a regular basis.1 Regularity matters as much as length; sleeping in at the weekend makes Monday tiredness worse.
- Stress, anxiety and depression: Mood is one of the most common — and most overlooked — causes of tiredness. Lasting low motivation deserves a conversation with a professional.
- Inactivity: It sounds backwards, but movement gives energy. In an analysis pooling controlled studies, regular exercise raised feelings of energy and lowered fatigue on average, though the effect was less clear in placebo-controlled trials.2
- Irregular eating: Skipping meals and getting by on sugary snacks leads to energy peaks and crashes.
- Not drinking enough: In an experiment with women, losing fluid equal to just 1.36% of body weight worsened mood, feelings of fatigue and concentration;3 in men, a 1.59% loss increased fatigue and tension.4
- Caffeine and alcohol: Late-afternoon caffeine and evening alcohol break up sleep, so the next day starts tired.
- Iron deficiency and anaemia: According to the World Health Organization, symptoms of anaemia include fatigue, weakness, dizziness and shortness of breath; it's especially common in women with heavy periods.5
- Other medical causes: Thyroid problems, diabetes, sleep apnea, recent infections and some medicines. Only tests and an examination can tell these apart.
How to tell how much hydration plays a part
Dark urine, thirst, headaches and concentration that drops in the afternoon are common signs of mild dehydration. Needs rise in hot weather, on long motorcycle rides and on training days. Dehydration is rarely the only explanation for tiredness, but it's the easiest to fix: drinking regularly for a week and watching for a difference also helps you rule the other causes in or out.
The NHS advises seeing a GP if you've been feeling tired for a few weeks and aren't sure why, and lists iron deficiency anaemia, diabetes, thyroid problems and sleep apnoea among the causes to check.6
Where to track this in Suu
Suu can't tell you why you're tired, but it makes the hydration and movement parts visible. Menu names are exactly as they appear:
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Suu Index
iPhone: You tab → Water → Suu Index
Android: Statistics → Suu IndexScores your daily hydration from 0 to 100, so on tired days you can see whether it was low instead of guessing.
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A goal that follows the weather
The Weather & info card on the home screen
Your daily water goal rises automatically on hot days and after workouts.
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Morning Reminders
iPhone: Settings → Notification Settings → Smart Notifications → 🌅 Morning Reminders
Android: Settings → Smart Notifications → 🌅 Morning RemindersReminds you to start the day with a glass of water — the easiest step after a night without drinking.
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Log your coffees too
The Suui assistant on the home screen
Just say "I've had my third coffee"; coffee counts partly as water (filter coffee 0.8) and late caffeine becomes visible. The free plan includes 3 AI messages a day.
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A 10-minute walk
Home → quick add → Add Exercise → Walking
Records a short GPS walk; within a few weeks your own log shows how movement affects your energy.
The short version
Constant tiredness rarely has a single cause: first take an honest week of notes on sleep, stress, movement, food, water and caffeine, and fix the easy ones.
If it doesn't improve within two to four weeks, or comes with weight loss, fever, shortness of breath or low mood, see a doctor without waiting. Simple blood tests often give the answer.
See your hydration, don't guess it
Suu Index, smart reminders and a weather-aware goal · free on iOS and Android
Frequently asked questions
Why am I always tired?
The most common causes are too little or poor-quality sleep, stress and low mood, inactivity, irregular eating, not drinking enough, and too much caffeine or alcohol. Medical causes such as iron deficiency, thyroid problems, diabetes and sleep apnea are also possible; see a doctor if tiredness lasts.
When should I see a doctor about tiredness?
See a doctor if tiredness lasts more than two to four weeks or comes with unexplained weight loss, fever, night sweats, shortness of breath, palpitations, low mood or heavy periods.
Can dehydration cause fatigue?
Yes. In experiments, losing fluid equal to only about 1.4–1.6% of body weight increased feelings of fatigue and worsened mood and attention. But dehydration is rarely the only explanation for tiredness.
What blood tests are done for tiredness?
That's your doctor's call; they usually start with a full blood count, iron stores (ferritin), thyroid hormones and blood sugar. Other tests may follow depending on your symptoms.
Does coffee help with tiredness?
It boosts alertness in the short term, but coffee late in the afternoon can disrupt sleep so the next day starts more tired. Keeping caffeine to the morning and early afternoon helps most people.
Can Suu find the cause of my tiredness?
No — Suu is not a diagnostic tool. It only makes one possible cause, fluid intake, visible through the Suu Index, and your movement visible through GPS walks. See a doctor to find the cause of your tiredness.
References
- Watson NF et al. — Recommended amount of sleep for a healthy adult: a joint consensus statement of the AASM and SRS. J Clin Sleep Med, 2015
- Puetz TW et al. — Effects of chronic exercise on feelings of energy and fatigue: a quantitative synthesis. Psychol Bull, 2006
- Armstrong LE et al. — Mild dehydration affects mood in healthy young women. J Nutr, 2012
- Ganio MS et al. — Mild dehydration impairs cognitive performance and mood of men. Br J Nutr, 2011
- World Health Organization — Anaemia (fact sheet)
- NHS — Tiredness and fatigue
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Suu is not intended for medical diagnosis or treatment. Consult a healthcare professional for health-related decisions.