Causes of Constant Tiredness or Fatigue

Constant tiredness and fatigue can stem from various causes that affect your energy levels throughout the day. These causes typically fall into four categories: lifestyle factors, medical conditions, sleep disorders, and mental health issues.

For example, excessive alcohol use or poor sleep hygiene can disrupt your routine and leave you feeling drained. Medical conditions like hypothyroidism, sleep disorders such as sleep apnea, or mental health issues like depression can also contribute to persistent fatigue.

Lifestyle Factors That Cause You to Feel Tired

Lifestyle can have a big impact on your daytime alertness and energy levels. Among the factors that you may want to discuss with a healthcare provider are:

• Diet: Your body gets energy from food, and an unbalanced diet or skipping meals can leave you feeling tired during the day. Diet-related causes of fatigue include deficiencies in zinc, vitamin B12, or vitamin D, blood sugar fluctuations, excessive alcohol, and too much caffeine.
• Dehydration: Dehydration occurs when you lose more fluids than you take in. Since water makes up 50% to 60% of your body weight, sweating, urination, heat, or illness can quickly deplete your hydration levels. While drinking eight 8-ounce glasses of water daily is a common guideline, vary—pale yellow or clear urine generally indicates proper hydration.
• Poor sleep habits: Daytime fatigue may result from not getting enough quality sleep. Poor habits like sleeping in a noisy or uncomfortable environment, skipping a bedtime routine, exercising too close to bedtime, or napping late in the day can disrupt your rest. Additionally, not meeting the sleep needs for your age (eight to nine hours a night for adults ages 18 to 60) can leave you feeling tired.
• Inactive lifestyle: A sedentary lifestyle can lead to restless, poor-quality sleep. Research suggests that regular physical activity improves sleep quality and mental health. In one study, participants who engaged in at least 150 minutes of moderate to vigorous exercise weekly for six months reported less insomnia, depression, and anxiety than those who were less active.
• Overexertion: Overexerting yourself through excessive exercise or other activities can leave your body too depleted to recover. This can lead to fatigue, poor sleep, and low motivation. Symptoms of overexertion may include mood swings, sore limbs, frequent illness, and a decline in performance at work or home.
• Stress: Psychological stress can disrupt your sleep, and poor sleep can, in turn, increase stress and fatigue. A survey found that 43% of adults had lost sleep due to stress in the prior month, and 37% reported feeling fatigued because of it. Research also shows that quality sleep helps maintain positive emotions during stressful events and enhances joy from positive experiences.

Medical Conditions That Cause You to Feel Tired

Fatigue, general weakness, and feeling sleepy are symptoms associated with many medical conditions. These conditions affect your energy levels. Symptoms of daytime sleepiness may be related to the following underlying causes:

• Anemia: Anemia is a condition in which your body has fewer red blood cells or they don’t function properly, reducing the blood’s ability to deliver oxygen to your organs. This can cause symptoms like fatigue, headaches, difficulty concentrating, irritability, and numbness in the hands and feet. The most common type is iron-deficiency anemia, but other causes include inherited disorders, chronic illnesses, and pregnancy.
• Autoimmune disease: Autoimmune diseases occur when your immune system mistakenly attacks your own body, causing tissue damage and chronic inflammation. Conditions like rheumatoid arthritis, lupus, multiple sclerosis, and inflammatory bowel disease can lead to fatigue and disrupt your metabolism, nervous system, and sleep patterns. They may also cause imbalances in cytokines, proteins that regulate inflammation, mood, and sleep.
• Cancer: More than 80% of people with cancer experience cancer-related fatigue, which often doesn’t improve with rest and can be an early sign of the disease. Fatigue can result from low blood counts, disturbed electrolytes, altered hormone or cytokine levels, and changes in cell function caused by cancer. Treatments like chemotherapy, immunotherapy, and radiation can also contribute to fatigue.
• Chronic fatigue syndrome: Chronic fatigue syndrome (ME/CFS) causes extreme fatigue that worsens with minimal exertion, doesn’t improve with rest, and often includes flu-like symptoms and cognitive issues like “brain fog.” The exact cause is unknown, but it may be linked to infections, chronic stress, autoimmune responses, or cytokine-related inflammation.
• Chronic obstructive pulmonary disease (COPD): This chronic disease causes wheezing, shortness of breath, and excess mucus, making it hard to breathe. Fatigue is common in COPD, but research suggests it may not always be directly tied to breathing difficulty. The disease progresses over time and is especially common in current or former smokers.
• Depression: This mood disorder causes sadness, loss of interest, and physical symptoms like fatigue. Daytime sleepiness may result from insomnia or other sleep problems often linked to depression, and fatigue may serve as an early warning sign. Biochemical similarities between depression and ME/CFS might explain fatigue as a shared symptom.
• Diabetes: Diabetes fatigue syndrome refers to persistent fatigue experienced by people with diabetes. Possible causes include low blood sugar, hormonal imbalances, treatment side effects, overlapping conditions, and lifestyle factors like diet.
• Fibromyalgia: Fibromyalgia is a chronic pain condition. It’s caused by dysfunction in the central nervous system, which heightens sensitivity and turns harmless sensations into pain or allodynia. Fatigue is also a key symptom of fibromyalgia. This fatigue may be due to biochemical changes, inflammation, sleep disorders, and sleep disruptions.
• Heart disease: If you have fatigue that’s new and constant, it may be an early warning sign of heart failure or, less often, coronary artery disease. These conditions limit the amount of oxygen-rich blood that gets to your muscles or to the heart itself. Your heart and brain need oxygen. When you have heart disease, your body limits the blood sent to less important parts like the limbs, leading to reduced energy and fatigue.
• Infections: Fatigue is common during and after infectious illnesses like COVID-19, influenza, mononucleosis, and Lyme disease. While tiredness often resolves as the illness clears, some people experience lingering fatigue, known as post-viral fatigue or, in the case of COVID-19, long COVID. Researchers are exploring links between these persistent symptoms and conditions like ME/CFS, especially for viruses like Epstein-Barr, which can reactivate and contribute to fatigue and autoimmune diseases.
• Food allergies and intolerances: Food allergies and intolerances can cause fatigue by triggering immune responses or gastrointestinal distress that deplete energy levels. Reactions to allergens, such as dairy, gluten, or nuts, may lead to inflammation, poor nutrient absorption, or disrupted sleep. Chronic exposure to problematic foods can worsen fatigue over time, especially if the underlying issue goes unaddressed.
• Kidney disease: Kidney disease can cause fatigue due to the buildup of toxins in the blood when the kidneys are not functioning properly. This can lead to anemia, as the kidneys produce less erythropoietin, a hormone essential for red blood cell production. Electrolyte imbalances and reduced nutrient absorption may also contribute to low energy levels.
• Menopause: The transition to menopause, including perimenopause and the early post-menopausal stage, often brings fatigue along with symptoms like hot flashes, night sweats, and mood swings. Fatigue may stem from sleep disruptions, hormonal changes, aging, or stress.
• Pregnancy: Pregnancy places extra demands on the body, often causing fatigue, especially during the first and third trimesters. Factors contributing to this tiredness include the energy required to support the baby, hormonal changes, low blood sugar or pressure, and disrupted sleep. Stress and digestive changes can also play a role in pregnancy-related exhaustion.
• Thyroid disease: Thyroid hormone imbalances, whether high (hyperthyroidism) or low (hypothyroidism), can cause fatigue due to their effects on metabolism. Hyperthyroidism speeds up bodily processes, leading to symptoms like anxiety, sleep disruption, and eventual exhaustion as energy reserves deplete, while hypothyroidism slows everything down, causing fatigue alongside weight gain, depression, and memory problems.

Sleep Disorders That Cause You to Feel Tired

Various circadian rhythm disorders can leave you feeling too sleepy during the day. The circadian rhythm is your body’s natural clock. It helps to coordinate your activities based on when it’s light and dark in your environment. If your internal timing is misaligned, you may find yourself with excessive daytime sleepiness.

Six common circadian rhythm disorders include:

• Advanced sleep phase syndrome: The distinguishing feature is falling asleep and waking up earlier than you want, usually by about three hours.
• Delayed sleep phase syndrome: This causes difficulty falling asleep and makes it extremely hard to wake up.
• Irregular sleep-wake rhythm: This occurs when the circadian rhythm becomes completely disconnected from the natural day-night cycle. Sleep is fragmented, with short spells scattered throughout the day.
• Jet lag: A temporary rhythm disorder associated with travel across several time zones. To adjust, it may take one day for every time zone you cross.
• Non-entrained (non-24) disorder: This usually occurs in visually impaired people. The sleep cycle is typically a little longer than average and thus becomes more out of sync every day.
• Shift-work sleep disorder: Poor sleep is caused by working at night and sleeping during the day. This can lead to increased accidents and possibly a higher risk of some forms of cancer.

Other sleep disorders that can result in constant tiredness or fatigue include:

• Insomnia: Insomnia, which makes it hard to fall or stay asleep, can be occasional or a chronic issue that causes constant fatigue. It may result from factors like genetics, irregular sleep schedules, stimulants, alcohol, drug use, or high stress levels. Environmental factors, sedentary lifestyles, and excessive light exposure, especially from screens before bed, can also contribute.
• Kleine-Levin syndrome: Kleine-Levin syndrome, a rare condition primarily affecting young men, causes recurrent episodes of excessive sleepiness that can last days to months and be severely debilitating. These episodes often disrupt daily life and school, with symptoms including hallucinations, hypersexual or compulsive behaviors, binge eating, and mood or cognitive disturbances.
• Narcolepsy: Narcolepsy disrupts the body’s ability to regulate sleep, causing sudden sleep attacks during the day and wakefulness elements during sleep. Key symptoms include cataplexy, a sudden loss of muscle control triggered by emotions, and vivid hallucinations during sleep transitions. Sleep paralysis, frequent nighttime awakenings, and performing actions during sleep attacks without memory of them are also common.
• Restless leg syndrome (RLS): Disorders causing excessive movements during sleep, like RLS, can disrupt sleep and lead to daytime fatigue. RLS creates an uncomfortable sensation in the legs and an urge to move, typically worsening in the evening or when lying down. Movement temporarily relieves the discomfort but can interfere with restful sleep.
• Periodic limb movement syndrome (PLMS): A condition related to RLS called periodic limb movement syndrome involves sudden jerking movements that occur during sleep. These may be repetitive, disturbing your sleep and potentially that of your bed partner.
• Sleep apnea: Sleep apnea causes repeated pauses in breathing during sleep, often followed by loud snorts or gasps that disrupt sleep cycles. These interruptions shift you into lighter sleep stages, leaving you tired even if you don’t recall waking. Symptoms include snoring, morning dry mouth or headaches, teeth grinding, sexual dysfunction, and frequent nighttime urination.

Medications That Cause Drowsiness

Drowsiness and fatigue are common side effects of medications. If you have daytime tiredness, your healthcare provider will likely look into what medications you’re taking. Drugs that can make you tired include:

• Analgesics: Painkillers including opioids such as Vicodin (hydrocodone-acetaminophen), OxyContin (oxycodone)
• Anticonvulsants: Seizure prevention drugs such as Neurontin (gabapentin) and Lyrica (pregabalin)
• Antidepressants: Tricyclics and SSRIs/SNRIs including Elavil (amitriptyline), Prozac (fluoxetine), Cymbalta (duloxetine)
• Antiemetics: Drugs for nausea, vomiting, and motion sickness such as Dramamine (dimenhydrinate), Zyprexa (olanzapine), Reglan (metoclopramide)
• Antihistamines: Allergy medications including Zyrtec (cetirizine), Claritin (loratadine), Benadryl (diphenhydramine)
• Antipsychotics: Drugs for schizophrenia, psychosis in bipolar disorder, depression, and Alzheimer’s disease including Abilify (aripiprazole), Risperdal (risperidone), Seroquel (quetiapine)
• Benzodiazepines: Tranquilizers and sedatives such as Librium (chlordiazepoxide), Valium (diazepam)
• Blood pressure drugs: Diuretics, ARBs, calcium channel blockers, beta-blockers including Lasix (furosemide), Avapro (irbesartan), verapamil HCL, Toprol-XL (metoprolol succinate)
• Muscle relaxants: Including Soma (carisoprodol), Lorzone (chlorzoxazone), Flexeril (cyclobenzaprine)
• Sedatives: Non-benzodiazepine sedative/hypnotics such as Ambien (zolpidem), Sonata (zaleplon), Lunesta (eszopiclone)
• Statins: Especially fat-soluble drugs including Lipitor (atorvastatin), Mevacor (lovastatin), Vytorin (ezetimibe/simvastatin), Zocor (simvastatin)
• Steroids: Used for inflammation, allergies, skin diseases, certain cancers, and after organ transplants. Some may cause insomnia, including prednisolone, methylprednisolone, dexamethasone

Summary

Feeling tired and sleepy during the day can result from certain illnesses such as diabetes, heart disease, or an autoimmune disorder. Many cases of fatigue are also related to dehydration, specific sleep disorders, or chronic conditions such as chronic fatigue syndrome. If you are experiencing constant tiredness or fatigue and do not know why, don’t hesitate to see a healthcare provider for an evaluation.