Extreme fatigue can be a warning sign of diabetes. Signs and symptoms of diabetes in addition to fatigue can include excessive thirst, frequent urination, blurred vision and recurring infections. A malfunctioning thyroid can cause fatigue. Hypothyroidism is a condition in which the thyroid gland fails to make or release enough thyroid hormone. The result is a mix of signs and symptoms, such as sluggishness, chronically cold hands and feet, constipation, dry skin and hoarse voice.
Hyperthyroidism is a condition in which the thyroid produces excessive amounts of hormone.
Too much hormone can cause fatigue, muscle weakness, weight loss, increased heart rate, nervousness and irritability. This blood disorder results from a number of problems that reduce your blood's ability to transport oxygen, causing fatigue. Fatigue can on occasion be a symptom of cancer. A thorough checkup, including routine cancer screenings, can help rule out malignancy as a cause of your fatigue. Persistent fatigue may be a symptom of an infectious illness, such as hepatitis, or slow recovery from influenza or pneumonia.