Not everyone has the exact same symptoms, but most people will have some degree of heat intolerance, unintentional weight loss, tremor, muscle weakness, hair loss, more frequent and looser bowels, anxiety, irritability or poor concentration. In younger women, the menstrual cycle will be less often and lighter. In more extreme situations, the heart can go into an irregular rhythm called atrial fibrillation. It also can result in weakened bone strength. In the worst cases, patients can develop a life-threatening condition called thyroid storm, which can cause high body temperature, fast heart rate, an altered mental status, heart failure, and possibly death.