Chronic fatigue can have many causes. It may also occur without any identifiable underlying cause like a medical condition or illness. Identifying the type of chronic fatigue can help doctors design better treatments.

Chronic fatigue
Chronic fatigue indicates fatigue that persists for a long time and does not go away quickly even with adequate sleep and rest.

Physical fatigue is the inability to initiate or complete any physical activity. Mental fatigue involves cognitive difficulties, inability to focus, and so on. Chronic fatigue can involve both of these.

Usually, fatigue or extreme tiredness goes away after a period of rest and good sleep. However, chronic fatigue is not so easy to shake off.

Medical conditions that may cause chronic fatigue
Many health conditions like diabetes, anemia, and cardiovascular diseases can cause chronic fatigue.

Diabetes: When patients have diabetes, they may experience a sharp change in their blood sugar levels, which may cause extreme tiredness. However, diabetic patients may also suffer from fatigue that is not linked to their sugar levels.

Cardiovascular diseases: Cardiovascular diseases weaken the heart muscles and impair the heart’s ability to pump blood. Thus, the regular blood circulation and oxygen supply are affected, leading to fatigue.

Cancer: Extreme tiredness can be a symptom of cancer. This illness can cause chronic fatigue, especially in the advanced stages. Cancer-related fatigue may also be a side effect of treatments like chemotherapy and radiation therapy.

Disorder of the nervous system: Patients who have suffered a stroke, or those who have Parkinson’s disease may also suffer from chronic fatigue.

If muscle weakness is a prominent part of your chronic fatigue issues, then the cause might be a neuromuscular disorder like muscular dystrophy, immune neuropathy, or metabolic myopathy.

Anemia: Anemia is a principal cause of chronic fatigue. In this condition, a patient has a low red blood cells count. Your red blood cells carry nutrients from food to various parts of your body, and hemoglobin in the red blood cells carry oxygen. A low red blood cell count affects these normal functions of blood circulation and causes exhaustion.

Hypothyroidism: In hypothyroidism, the thyroid glands are unable to produce adequate amounts of the thyroid hormones that are essential for various functions of the body. Fatigue is one of the identifying symptoms of hypothyroidism, accompanied by muscle weakness, acute sensitivity to cold, skin dryness, and so on.

Many other medical conditions like endocrine disorders, chronic infections like HIV and tuberculosis can also cause chronic fatigue

Other causes of chronic fatigue
Sometimes, many people suffer from chronic fatigue without having an underlying condition.

Chronic Fatigue Syndrome (CFS)
If a patient reports chronic fatigue and after diagnostic tests for possible causes, no medical condition is identified, the patient is said to be suffering from Chronic Fatigue Syndrome or CFS.

Symptoms of CFS

• Fatigue
• A headache
• Cognitive difficulties like verbal dyslexia
• Memory loss
• Feeling exhausted after even slight physical exertion
• Sleep does not have the usual effect of healing tiredness and making you feel fresh and energized

For a CFS diagnosis, the symptoms have to fulfill certain conditions:

• More than six months of experiencing associated symptoms like memory loss, post-exertional malaise, cognitive difficulties
• Unrefreshing sleep

Causes of CFS
Chronic fatigue syndrome is also referred to as systemic exertion intolerance disease or myalgic encephalomyelitis (ME). It is also known as ME/CFS. CFS can have many causes, though none have been identified as a significant trigger. Some of the possible causes are:

• Genes:  Some people have a genetic predisposition to CFS.
  Virus: Certain viral infections like human herpesvirus 6, and Epstein-Barr virus can cause this condition.
• Immune system disorders: Autoimmune disorders like rheumatoid arthritis and other immune system dysfunction like an overactive immune system can be probable causes of chronic fatigue.
• Allergies: Sometimes, allergies can trigger the immune system to produce excess amounts of cytokines which are chemicals that control the immune system functions. Thus, allergies can cause chronic fatigue.
• Neurotransmitter issues: In some ME/CFS patients, low levels of the neurotransmitters dopamine and serotonin have been identified. Ongoing research is attempting to find out about the role of these neurotransmitters in causing CFS
• Cortisol deficiency: Cortisol is a hormone that has many vital functions in the body, but it is most popularly called the “stress control hormone” because it is released in response to stress. It initiates many functions that help to reduce the effect stress has on the body. Deficiency in this hormone may be one of the causes of chronic fatigue syndrome.
• Gender: Generally, CFS is associated with women because the majority of patients who report the symptoms of CFS are women. While research is attempting to identify if women are predisposed to CFS, many believe that this skew may have social causes. Men may not report such symptoms like muscle weakness and chronic tiredness because gender-based roles have conditioned them to act tough and not confess about any weaknesses.
• Fibromyalgia
  It is a chronic pain disorder, and like CFS, it has no identified causes. Fibromyalgia can be a cause of chronic pain and fatigue. Recent imaging techniques that have given medical professionals better and more detailed views of the brain. Thus, medical professionals now have a better understanding of this condition. Recent research suggests that fibromyalgia is associated with a dysfunction in the pain regulation mechanism of the brain.
• Other possible explanations like nutritional deficiencies, exposure to environmental and chemical toxins, and disturbed circadian rhythm are being explored.

CFS has no identifiable cause and so is difficult to diagnose and treat. Research is trying to find out about the causes of chronic fatigue. If patients talk to their doctor about their symptoms, they can get the right treatment.