Hashitoxicosis is the hyperthyroid phase of Hashimoto's thyroiditis, which is an autoimmune disease involving gradual thyroid failure. It occurs when there is destruction of the thyroid follicles by an inflammatory process, leading to the release of preformed thyroid hormones into the bloodstream. Patients with Hashitoxicosis may experience symptoms of hyperthyroidism such as increased heart rate, weight loss, tremors, and anxiety.