Fatigue, defined as a lack of energy, is a common complaint, and can be caused by a host of medical or emotional reasons. According to Better Health Channel, fatigue can usually be traced to a habit, routine or lifestyle with poor nutrition, stress and insufficient rest often playing roles. Less commonly, fatigue can indicate a serious underlying medical condition. MayoClinic.com notes that you should see your doctor if fatigue persists in spite of getting enough sleep, proper nutrition, and making positive lifestyle changes.
Infections
Bacterial and viral infections can cause fatigue. According to Health Central, influenza strikes about 25 million people a year. Although influenza normally resolves in three to 7 days, it can cause severe fatigue, as well as fever, aches and chills. AIDS, the final stage of HIV infection, can also feature persistent fatigue as a symptom, as can pulmonary tuberculosis, a contagious bacterial infection involving the lungs. Fatigue, accompanied by sore throat and swollen glands, is also a classic symptom of mononucleosis, an infection caused by the Epstein-Barr virus.
Hypothyroidism
Another medical cause of fatigue is hypothyroidism, also known as underactive thyroid. According to MayoClinic.com, hypothyroidism results from inflammation of the thyroid gland, which can be caused by an immune system malfunction, a congenital defect, radiation treatments, or a virus. Fatigue, sluggishness and lethargy--along with joint pain, constipation and thinning, brittle hair--are symptoms of an underactive thyroid. MayoClinic.com says that symptoms tend to develop slowly, often over a period of years, and that the condition is more common in women and people over age 50.
Adrenal Disease
Addison's disease occurs when the adrenal glands, located on top of the kidneys, don't produce enough hormones. This is usually due to damage to the adrenal cortex, or outer portion of the gland, resulting from infection, autoimmune disease, tumors, or use of anti-coagulant drugs. Symptoms of Addison's disease include extreme weakness and fatigue, along with unintentional weight loss, slow movements, and chronic diarrhea.
Congestive Heart Failure
Fatigue can be a symptom of congestive heart failure. According to the National Institutes of Health, congestive heart failure can develop either slowly or abruptly and can involve one or both sides of the heart. A major cause of heart failure is coronary artery disease, in which the small blood vessels leading to the heart become narrowed, thereby causing insufficient blood and oxygen to reach the heart. Other causes are congenital heart disease, heart attack, infections, and arrhythmias, or abnormal heartbeats. Fatigue, especially when accompanied by feelings of weakness, faintness, and shortness of breath, can be an indication of congestive heart failure.
Diabetes
Fatigue can be a tip-off to diabetes, a disease in which your body is either resistant to insulin, which controls blood sugar, or makes insufficient amounts of it in the pancreas. The National Institutes of Health states that while type 1 diabetes is usually diagnosed by age 20, type 2 diabetes can develop in adulthood, often due to obesity and failure to exercise; many people with diabetes are unaware that they have the disease. Fatigue, especially if accompanied by irritability, excessive thirst, increased urination and blurred vision, can be an indication of type 2 diabetes.
