What are the most common symptoms of hyperthyroidism?

Multiple organs...: The thyroid hormones secreted by the gland affects almost every system, including basal metabolism, skin, heart, brain, bowel. The thyroid gland is controlled by a part of the pituitary/hypothalamus gland in the brain in a feedback mechanism (as with all glands). Increased thyroid hormone can be associated with 'poppy' eyes, racy pulse, moist skin, perspiring, diarrhea. See prior answer.

Most common: The most common symptoms are fatigue, difficulty sleeping, irritability or nervousness, increased sensitivity to heat, & sometimes fast or irregular heart rhythm. Other symptoms may include hand tremors, muscle weakness, shortness of breath, increased appetite, hair loss, diarrhea, & change in vision or eyes.