What are some symptoms of hyperthyroidism and why is it bad?

Cardiac. The biggest risk is atrial fibrillation which is a cardiac rhythm problem. This is a rapid heart. There are serious side effects of atrial finrillation which is why it is bad. Be of the rapid heartbeat, there's a risk of blood clotting and even stroke. There can also be effects on the fetus, the baby, and risk of miscarriage if you are pregnant. There can also be weight-loss due to wasting syndrom.