She was plagued first by hyperthyroidism, which sped up her metabolism and prevented sleep. Oprah eventually "blew out" her thyroid and experienced classic symptoms of hypothyroidism: Her metabolism slowed and she felt sluggish and tired.
After discovering the cause of her health problems, Oprah decided this was a wake up call. She was determined, not only to get back in balance, but to highlight this particular women's health issue. According to The Wisdom of Menopause author Dr. Christiane Northrup, 25 percent of perimenopausal and menopausal women experience some kind of issue with their thyroid at some time, and most women don't know the cause of their deteriorating health.
I, for one, hope that with Oprah highlighting this issue that it receives more attention, both in research and educational outreach. You know Oprah knows how to stir things up! You can read much of the article, which explores the "break down to break through" moments of personal health, online at Oprah.com – hopefully it will help you learn to listen to your body.