If left untreated, Graves’ Disease can lead to heart problems and problems in pregnancy, and an increased risk of a miscarriage. Severe, untreated Graves’ Disease can be fatal. Thyrotoxic storm is a rare life-threatening condition that develops in cases of untreated hyperthyroidism. It is usually brought on by an acute stress, such as trauma surgery or infection. Symptoms are severe, with a pounding heart, sweating, restlessness, shaking, diarrhea, change in consciousness, agitation and confusion. Congestive heart failure can develop rapidly and lead to death.