Hashimoto's thyroiditis is an autoimmune disorder that attacks the thyroid gland, causing inflammation and an underactive thyroid, resulting in hypothyroidism. It primarily affects middle-aged women and its main symptom is swelling of the throat. Other symptoms include fatigue, dry skin, constipation, muscle aches, and enlarged tongue. If left untreated, it can lead to complications like heart problems, decreased libido, birth defects, and myxedema.