The problem Amy Rangel, 54, has long lived with postural orthostatic tachycardia syndrome (POTS), a condition marked by a racing heartbeat, fatigue and dizzy spells. Last year, Rangel, then a math lecturer at Northern Arizona University in Flagstaff, was suffering so much that her doctors recommended she stop working. When she applied for short-term disability, however, her group insurance carrier denied the claim, asserting that she’d failed to show she couldn’t do her job.