I had just given birth to my third child when I started showing symptoms of an adrenal gland tumor. I wasn’t actively ill. But I felt weak, anxious and crushed with fatigue. My heart was beating too fast, and my legs were walking too slowly. I couldn’t concentrate on anything. The world felt upside down.

Since I’d recently had a baby, I assumed at first that my hormones were still out of whack. I attributed my fatigue to both that...