The Thyroid Gland can produce either too little hormone or too much. Signs of an overactive thyroid gland which causes a condition called Hyperthyroidism include the following:

Hyperthyroidism Symptoms
Nervousness
Irritability
Difficulty Sleeping
Bulging eyes
Goiter or enlarged thyroid gland
Increased Sweating
Intolerance to Heat
Unexplained weight loss
Frequent Bowel Movements
Tremor in Hands/Fingers