You are a machine, sucking in oxygen and burning up glucose to order to fuel your brain and muscles. The machine's speed is driven by hormones secreted from an unlikely spot -- the thyroid gland straddling the base of your throat. Under gentle guidance from your hypothalamus, the thyroid normally does a good job of balancing your energy needs -- until you develop Graves' Disease.

Like most "autoimmune" illnesses, Graves' Disease tends to strike young women. Errant antibodies from your own immune system can target sensors in your thyroid, blinding its feedback mechanism and causing progressive weight loss, diarrhea, agitation and uncontrolled thoughts -- even psychosis. Because the illness creeps insidiously on its victims, your symptoms may be far advanced before they come to the attention of a doctor. The thyroid can swell, turning into a visible bag-like lump in your neck. As your thyroid hormone reaches toxic levels and your body's metabolism races terrifyingly out of control, your heart may outstrip its rhythm and your eyes bulge from their sockets. In the final and most dreaded stage of thyrotoxicosis, you may experience "thyroid storm," where high fever, heart failure and even death can result without medical intervention.

Your runaway thyroid can only be reined in by a carefully orchestrated series of drugs that counteract the hormones' effects. The final step may be to drink a "cocktail" containing radioactive iodine. This element is rapidly concentrated within the thyroid, and the short-lived radiation of the ¹³¹I isotope kills the rogue gland forever.

Deprived of your thyroid, you must now depend upon supplemental thyroid hormone pills for the rest of your days, but at least you will have been allowed to dismount from the wildest and most perilous ride of your life.

But don't forget to take your Synthroid, or your metabolic machine may slip the other way -- into the lethargic grip of myxedema coma!