It's not surprising it took a while for Sean to receive the proper diagnosis. Insulinomas are rare — one to four new cases per one million people per year — and are more common in people 40 and older. As in Sean's case, 20 percent of patients are initially diagnosed with a neurologic or psychiatric disorder before the insulinoma is recognized. A simple blood test at the time of symptoms would have solved this mystery. Sean had many blood tests in the course of his disease, but they were performed when he had eaten and showed no symptoms. Because hypoglycemia comes and goes and is triggered by fasting, timing of the blood sample is important.