Subclinical hyperthyroidism is a condition in which the thyroid gland is overactive, but no symptoms are present. Left untreated, however, subclinical hyperthyroidism can lead to serious health problems. That’s why it’s important to be aware of the symptoms of subclinical hyperthyroidism so you can get treatment if necessary. Some common symptoms of subclinical hyperthyroidism include anxiety, irritability, weight loss, and fatigue. If you experience any of these symptoms, see your doctor for a diagnosis.