If the client is still undiagnosed after the arrest, they should be instructed to obtain an examination as soon as possible. The records of the examination, with the proper certificate, may be admissible. This is especially true in accident cases, where the defendant frequently underestimates the existence of or extent of injury. In a recent case, a defendant received a diagnosis of a concussion shortly after an accident that resulted in arrest. This evidence should help to show that the accident likely caused the apparent impairment of normal coordination that was observed by the arresting officer.
Many clients have health problems that can constitute exculpatory evidence in a drunk driving case.
It often does not occur to the client that the particular medical condition constitutes a defense, especially if they believe themselves to be guilty. Nevertheless, when it is possible to present such a defense without the defendant testifying, that belief is irrelevant.