Fatigue is described as an intense feeling of tiredness and lack of energy that results in an ability to perform daily tasks. Fatigue is often accompanied by weakness, which can be physical muscle weakness or a mental weakness that is characterized by a decreased desire to partake in activities. Fatigue and weakness can indicate underlying physical or mental disorders.
Anemia
Red blood cells are responsible for binding oxygen and delivering that oxygen to all of the tissues in the body. Anemia is a condition in which the body does not contain enough healthy red blood cells. If certain vitamins and nutrients are not available in the body, red blood cells cannot be made properly. There are various types of anemia, but the most common are iron-deficiency anemia, which develops due to a lack of iron, and pernicious anemia, which develops due to a lack of the vitamin B12. Without enough healthy red blood cells in the body, an adequate amount of oxygen cannot be delivered to the body tissues. A lack of oxygen leads to fatigue and weakness.
Insomnia
Insomnia is a sleep disorder characterized by an inability to fall asleep or stay asleep. Sleep is the body's tool for re-energizing and re-fueling the cells. Without an adequate amount of sleep, the body becomes drained and cannot function properly. Insomnia can cause fatigue and weakness, as well as mental confusion and inability to think clearly.
Thyroid Disorders
The thyroid gland is a small gland located in the front of the neck that is responsible for producing thyroid hormones, which help maintain a number of body functions, including metabolism and temperature. Hyperthyroidism is a medical condition in which the thyroid gland produces too much thyroid hormones. Hypothyroidism is a medical condition in which the thyroid gland does not produce enough thyroid hormones. An imbalance of thyroid hormones can cause a number of symptoms, including fatigue and weakness.
Hypoglycemia
Hypoglycemia is a condition that occurs when the levels of glucose in the blood fall below 70 mg/dL. Glucose provides the body with energy needed to perform daily tasks as well as maintain biological functions. When blood sugar falls too low, it can be harmful to the body. Hypoglycemia often leads to fatigue and weakness, as well as lightheadedness, cognitive difficulties and increased heart rate.
Dysthymic Disorder
Dysthymic disorder is a mild to moderate form of depression that lasts for at least two years. The American Academy of Family Physicians notes that dysthymic disorder is a common type of depression that usually affects women, but can affect any one. Symptoms of the disorder include fatigue, low energy, weakness, changes in eating habits and changes in sleeping habits.
Mononucleosis
Mononucleosis, which is commonly referred to as the kissing disease, is a viral infection caused by the Epstein-Barr virus. When the virus enters the body it can cause fatigue and weakness as well as sore throat, fever, swollen lymph nodes, swollen tonsils, headache, loss of appetite, inflammation of the spleen and night sweats. Mononucleosis is contagious, so it is important to avoid contact with other individuals while symptoms persist.
