"On our third year clinical rotations, she developed hives. It was strange. We immediately assumed the role of medical student detective, trying to determine the source. She tried the non-latex gloves in the OR, to no avail. I remember one weekend, we decided to put all of the plants in her apartment on her back porch, to see if they were the culprit. We regarded her fish Kumar, named after the author of our second year pathology text, suspiciously - even though he was an unlikely candidate for her troubles.
The hives worsened, and became a chronic problem. She visited an allergy-immunology expert, and was loaded up on a triple-drug regimen, in order to try to gain relief on a Christmas visit with her parents to visit her brother in Italy. One night, shortly after returning from Christmas vacation, she called me frantically from the grocery store.
"I am standing in the aisles, looking at the signs for aisle content, and I can't read them. They're blurry. I've always been able to read the signs. What can this mean? I'm scared."
She went to an ophthalmologist, the next week. The ophthalmologist listened to her history, gave her an eye exam, and told her - let's look at your sugar. I am worried. It was sky high. She was diagnosed, in her early twenties, with Type 1 diabetes, about six months after her hives presented. As soon as her diabetes was treated, her hives disappeared."

Diagram (mind map) of acute urticaria (click to enlarge the images).

Diagram (mind map) of chronic urticaria (click to enlarge the images).
References:
Trying to Diagnose Disease - Med Student Style. Mothers in Medicine, 2010.