Top Causes of Unexplained Fatigue (SQ-151)
Most of us have experienced days when we feel too exhausted to get out of bed and it feels like you have no energy to get through the day. Long and stressful days at work, physical exertion, lack of sleep and infections such as cold and flu might be the reason you feel so tired and sleepy and devoid of energy on some days. Feeling tired is common, but it is usually fixed with good rest and sufficient sleep.
What about overwhelming fatigue that doesn't seem to go away, no matter how well you have slept the previous night? Symptoms such as sudden and extreme tiredness that comes along with frequent headaches, unexplained muscle fatigue, joint pain, poor mood and unintended weight loss could be a sign of a medical problem and should be addressed immediately.
In this article we are going to explore the symptoms and primary likely causes of unexplained fatigue, a feeling that is something more than just being tired, sluggish and sleepy on some days.
Symptoms of chronic fatigue
- Fatigue that doesn’t improve with rest and sleep
- Lack of energy
- Lack of motivation or interest
- Excessive daytime sleepiness
- Joint pain
- Muscle pain, aches and weakness
- Brain fog
- Mental fatigue
- Sore throat and flu-like symptoms
- Frequent headaches
- Trouble sleeping
- Swollen lymph nodes
- Impaired memory
Primary likely causes of unexplained fatigue
Chronic fatigue is when you experience an ongoing feeling of tiredness that interferes with your daily routine, work performance and even social relationships. There can be many reasons behind fatigue, and these may range from nutritional deficiencies to dehydration and to sleep problems and health conditions such as thyroid disorder and diabetes. Let’s look at some of the common causes of unexplained chronic fatigue.
1. Nutritional deficiencies
Nutritional deficiencies caused by unhealthy diet, restricted diet and certain health conditions such as celiac disease can cause extreme fatigue. If not addressed, these nutritional deficiencies can lead to even more devastating health consequences such as weak bones, poor immunity, impaired cognition and even depression. For example, a severe B12 deficiency can cause extreme fatigue, severe depression, brain fog and memory loss. And a chronic vitamin B12 deficiency can even cause irreversible brain and nervous system damage, if left untreated for long.
- B vitamins, such as vitamins B12, B6 and folic acid, are particularly known for their role in energy production. Vitamin B12 is required for making healthy and mature red blood cells and its shortage can lead to vitamin B12 deficiency anemia with symptoms such as fatigue, lethargy, skin pallor, confusion and shortness of breath. Vegetarians are more prone to developing B12 deficiency but people with absorption issues and those with a history of abdominal surgery that removes some or all parts of the small intestine can develop B12 deficiency. Deficiency in Vitamin B6 can also leave you feeling overly exhausted. It shouldn’t be a surprise as B6 is involved in the production of haemoglobin and its shortage can cause microcytic anemia. Other symptoms of low B6 include poor mood, irritability, confusion, lack of energy, muscle fatigue and chronic pain.
- Magnesium plays a very critical role in the process of energy production. Along with fatigue, muscle weakness, muscle cramps, frequent migraine and loss of energy are some other common symptoms of magnesium deficiency. Whole grains, nuts, seeds, and leafy greens are good sources of magnesium. But poor diet, persistent infections, chronic stress and excessive intake of alcohol may deplete this important mineral from the body, leaving you feeling sluggish and tired.
- Iron is required to make haemoglobin, an important protein in red blood cells that helps them to carry oxygen throughout the body. If your body is lacking in iron, it won't be able to produce enough healthy red blood cells and your tissues and organs won't get enough oxygen to work properly. This is called iron deficiency anaemia, with symptoms such as extreme fatigue, dizziness, shortness of breath, cold extremities, chest pain, pale skin, headache and muscle pain.
- Vitamin D deficiency can cause extreme fatigue in the body. Joint pain, muscle aches and reduced energy levels are some other signs that you may be low in vitamin D. Supplementation with vitamin D3 can improve fatigue in people who are otherwise healthy but have vitamin D deficiency.  Your body can make vitamin D when the skin is exposed to sunlight. While daily exposure to sun may not be possible for some people, taking high quality vitamin D supplements can ensure your body has sufficient vitamin D to keep your immunity, bone health and heart health in order.
2. Stress and depression
Chronic fatigue is one of the most telling symptoms of mental health issues such as depression. In fact, fatigue often contributes to a long-lasting and deeper depression as it makes it really hard for an affected individual to take steps that can help them get a handle on their condition, such as going out for a walk and exercise. People with depression experience severe mental and physical fatigue and they often struggle with performing even simple day-to-day activities.
Prolonged stress also causes chronic fatigue, mental exhaustion and inability to sleep well, which further causes reduced energy levels and weakness. Postpartum depression is another serious problem that can affect new mothers, causing overwhelming fatigue and lethargy. Other signs may include severe mood swings, extreme sadness, excessive crying, insomnia and panic attacks.
3. Physical health conditions
Persistent fatigue can also be a result of health conditions such as thyroid problems, diabetes, fibromyalgia, electrolyte imbalance, kidney problems and lung disease. Pregnancy, breastfeeding and use of oral contraception can also make you feel extremely tired. Let's go through some common health conditions where fatigue is often a very prominent symptom.
- Heart disease, especially congestive heart failure, can be a reason why you are feeling unreasonably tired all the time. If simple physical activities like walking or climbing is draining your energy and leaving you with extreme exhaustion and shortness of breath, it could be a sign of heart disease. The main function of your heart is to pump blood throughout the body to deliver oxygen and nutrients to cells and tissues. In heart failure, the heart stops functioning properly and as a result not enough blood reaches your muscles, brain and other tissues, leading to fatigue. If you are experiencing extreme fatigue in combination with symptoms such as chest pain, swollen legs and ankles, impaired ability to exercise, shortness of breath, jaw pain, persistent cough or tightness in chest and throat, it is best to rule out the possibility of congestive heart failure with a visit to your healthcare professional.
- Excessive fatigue is one of the early warning signs of an underlying thyroid disorder.  People with hypothyroidism, where the thyroid gland produces insufficient amounts of thyroid hormones, often feel too tired, lethargic and low on energy all the time. Other symptoms may include muscle weakness, tender muscles and painful joints. Slow metabolism in hypothyroidism often results in other signs such as dry skin, weight gain, irregular periods, thinning of hair and constipation. Hyperthyroidism, where an active thyroid gland produces more hormones than required, can also cause fatigue that often results from insomnia and anxiety.
- Cushing's syndrome, where your body makes excessive levels of cortisol, and Addison’s disease, a condition that causes hormonal imbalance in the body, are potential and often overlooked causes of fatigue.
- High blood sugar levels and complications associated with diabetes can cause extreme fatigue.  In type 2 diabetes, the cells can't absorb glucose that is floating in the bloodstream, resulting in blood glucose levels that are abnormally high. Poor cellular functions result in reduced energy and overall fatigue. Inflammation and lifestyle factors also contribute to fatigue in diabetic patients. 
People with diabetes often experience increased urination and frequent trips to the bathroom. This not only causes dehydration but also keeps one awake at night, causing fatigue. Complications that often coexist with diabetes, such as heart disease, kidney problems, obesity, stress and depression can all contribute to persistent fatigue.
- People suffering from various forms of arthritis such as rheumatoid arthritis and psoriatic arthritis often report fatigue as one of the major and disabling symptoms that disrupts their daily lives [5-8]. Chronic inflammation and chronic joint pain in people with arthritis can leave one feeling extremely weary and tired throughout the day. Painful joints also make it difficult to sleep at night, contributing to the vicious cycle of pain, insomnia and total lack of energy. In addition, people with rheumatoid arthritis are prone to developing depression that is a potential trigger for fatigue and exhaustion.
- Extreme fatigue can also be a sign of fibromyalgia, a condition with other hallmark symptoms such as widespread musculoskeletal pain, sleep disruption, memory issues, difficulty thinking and mood swings. Disrupted sleep and chronic pain are likely reasons for fatigue and ‘fibro fog’ in fibromyalgia. Living with chronic pain and resulting fatigue and poor sleep can also lead to depression and anxiety, which leads to more exhaustion and lack of energy in individuals with fibromyalgia.
4. Insomnia and other sleep disorders
Both short-term and chronic insomnia can cause excessive daytime sleepiness, fatigue and irritability. If you are having trouble falling asleep or staying asleep, or if you are finding yourself waking up too early, it can make you feel extremely tired throughout the day affecting mood, immunity, work performance, decision making and concentration.
Stress, depression, anxiety, chronic pain, working night shifts (irregular sleep patterns), unhealthy sleeping habits, use of alcohol and drugs, and neurological conditions such as Parkinson's disease and Alzheimer's disease are some top causes of insomnia. Hormonal imbalances triggered by thyroid issues and menopause can also make it difficult falling or staying asleep. In addition, other sleep disorders like sleep apnoea and restless leg syndrome can also cause insomnia in some people.
Food intolerance could also be a reason behind your constant feeling of tiredness, especially when you don't have any other underlying medical condition such as thyroid disorder, cancer, diabetes or arthritis. People who are intolerant or insensitive to certain foods can struggle with exhaustion and brain fog after eating such food items. If you have been experiencing chronic fatigue that you cannot account for, it may be a good idea to get tested to find out if you are allergic or intolerant to any food.
Feeling unusually tired can be a sign that you are dehydrated. Being well-hydrated is important for your body to function properly. Proper hydration keeps your blood circulation healthy, improves sleep, keeps organs and tissues healthy and supports detoxification. Even mild dehydration can cause fatigue, reduced energy levels and other symptoms like muscle cramps, headache and light-headedness.
Excessive thirst, dry mouth, dizziness, dry skin, dark coloured urine and urinating too little are some signs that your body may be dehydrated. Not drinking enough water, diarrhea, vomiting, fever, use of diuretics, alcohol and excessive sweating can cause dehydration, leaving you with poor physical strength and feelings of fatigue and weakness.
7. Drugs and medications
Many common drugs and prescription medication are known to cause fatigue. Anti-histamines, antidepressants, antibiotics, beta blockers (drugs that are used to reduce high blood pressure), statins (cholesterol lowering drugs), and pain-relieving drugs are some of the common drugs that can cause physical and mental fatigue, sleep disturbances, and loss of energy. Drugs used for substance withdrawal (alcohol, pain medications and illegal substances) can also cause excessive sleepiness, extreme exhaustion, muscle fatigue and flu like symptoms.
When should I be worried about my fatigue?
Sometimes, getting rid of fatigue and exhaustion can be as simple as addressing a nutritional deficiency or eating healthy and getting good amounts of rest and sleep. But you should consult your healthcare professional if you are experiencing sudden fatigue with unintended weight loss, have trouble falling asleep or notice signs of depression. In addition, symptoms like shortness of breath, rectal bleeding, pain in the chest and elsewhere in the body along with chronic fatigue and sleepiness could be warning signs of a serious medical condition that needs to be diagnosed and addressed immediately.
If your fatigue has persisted for more than two weeks, even after you have rested well and taken care of your nutrition, it is time to see a doctor to find out if an underlying medical condition could be the reason behind your fatigue and associated symptoms.
- Nowak et al. Effect of vitamin D3 on self-perceived fatigue. Medicine (Baltimore). 2016
- Chaker et al. Hypothyroidism. Lancet. 2017
- Sanjay Kalra and Rakesh Sahay. Diabetes Fatigue Syndrome. Diabetes Therapy. 2018.
- Yaxin Bi et al. Contributing factors of fatigue in patients with type 2 diabetes: A systematic review. Psychoneuroendocrinology. 2021.
- Janet E Pope. Management of Fatigue in Rheumatoid Arthritis. RMD Open 2020.
- Santos et al. The impact of fatigue in rheumatoid arthritis and the challenges of its assessment. Rheumatology. 2019
- Raygaerts et al. Effect of biologics on fatigue in psoriatic arthritis: A systematic literature review with meta-analysis. Joint Bone Spine. 2018.
- Tuncay et al. The impact of fatigue on patients with psoriatic arthritis: a multi-center study of the TLAR-network. Rheumatology International. 2020.