Unlike other diseases that build over time, people rarely see symptoms early on or if they do, simply ignore them. The symptoms don't jump out at you like other diseases. There are rarely sudden emergency room visits or debilitating problems that lead to a quick diagnosis. Most people learn they have or are one the verge of diabetes from a standard doctor's appointment.
Diabetes is a silent disease and doctor's realize this and is why a glucose check is part of the standard battery of tests a doctor does during a regular checkup. When he discovers your elevated glucose levels he puts his diagnosis into overdrive.
Without these regular doctor's appointments, people can live on the verge of diabetes or actually with diabetes for years and never even know. It's slowly wrecking their body and without proper diet and control, it can lead to serious symptoms. By the time, it is diagnosed because of a major problem it may be too late to control it with diet and exercise.
Odds are you dismissed the headaches, frequent urinations and constant thirst as nothing at all and it wasn't until things became more frequent or more severe that you finally went to the doctor. It's important to keep in close contact with your doctor and provide him with as much information as possible.