From the Land Mines in Accident Cases section of How You Can Avoid Legal Land Mines by Joseph S. Lyles (2003).
People who have been injured in an accident sometimes fail to mention all their problems to their doctor. For example, it is common for someone whose neck or back was injured in a collision to have headaches and insomnia. If the injured person mentions neck or back problems, but fails to mention the other problems, then the doctor surely won’t document those other complaints in his or her records. Later when the insurance company adjuster is reviewing the claim, he will not consider the headaches or insomnia because there is no reference to them in the medical records.
As far as insurance adjusters are concerned, if it is not written in the medical records, it didn’t happen. And if it didn’t happen, you will not be compensated for it by the insurance company.
The Lesson: Your failure to mention all your injuries to your doctor will prevent you from being adequately compensated for those injuries.