8 Surprise Reasons You're Still Tired

Your Thyroid Has Turned into a Slacker—or an Overachiever

You know the connection between fatigue and hypothyroidism, when an underactive thyroid doesn't produce enough metabolism-regulating hormones, so you may already be on the lookout for an unexplained weight gain and a slower-than-average heart rate. But you can also feel wiped out by hyperthyroidism, the opposite condition, says Sandra Fryhofer, MD, an Atlanta internist and past president of the American College of Physicians. "Your body is so revved up from the hormones that you end up feeling exhausted," Fryhofer says. An estimated 1 in 8 women will develop a thyroid disorder at some time, according to the American Thyroid Association, so talk to your doctor about tests that measure the amount of thyroid-stimulating hormones in your blood.