Hi & Welcome. I can understand your concerns. It is not normal to have fluctuation in thyroid hormone levels. Fluctuation in thyroid hormone levels are suspicious of underlying autoimmune thyroid disease which can produce stimulating or blocking antibodies. Fluctuating thyroid function can be defined as a spontaneous shift of functional thyroid state from hypothyroidism to hyperthyroidism or vice versa. In autoimmune thyroid disease, thyroid function can fluctuate. Thyroid-stimulating immunoglobulin stimulates the thyroid gland while blocking antibodies do the opposite. At a particular point, it is the balance between the two antibodies that decides the functional thyroid state. Since you had symptoms of overdose of Levothyroxine the treatment was discontinued as palpitations, tachycardia, increased pulse and blood pressure may be harmful while suffering from atrial fibrillation. You need to undergo thyroid function tests along with testing for those antibodies responsible for the fluctuation. Hope this will help you.