Final answer:
Hypothyroidism is characterized by low levels of thyroid hormones and can cause symptoms such as weight gain and fatigue. Hyperthyroidism, on the other hand, is characterized by excessive levels of thyroid hormones and can lead to symptoms such as weight loss and increased heart rate.
Step-by-step explanation:
Hypothyroidism occurs when the thyroid gland produces insufficient amounts of thyroid hormones. Symptoms of hypothyroidism include weight gain, tiredness, cold intolerance, and slow heart rate. Treatment usually involves thyroid hormone replacement therapy. In contrast, hyperthyroidism occurs when there is an overproduction of thyroid hormones and can result in weight loss, excessive body heat, increased heart rate, and bulging eyes. Treatment for hyperthyroidism varies depending on the underlying cause.