A naturopath doctor, right, treats a patient at her office. (Elaine Thompson/AP)

While awaiting a morning appointment in his office a few years ago, Marvin Lipman, Consumer Reports’ chief medical adviser, heard the screech of brakes followed by a loud crash. He rushed outside to find the would-be patient, a 60-year-old accountant, slumped over the steering wheel of his car, which had all but demolished a parked van. The man’s speech was slurred and he appeared dazed as he was loaded into an ambulance.

Rewind the tape to three years earlier, when the patient began having spells of anxiety, a rapid heartbeat and sweating every few months. In between episodes he was perfectly fine. Eventually another symptom appeared: bouts of abusive behavior toward his wife, who learned that she could calm him down by feeding him sweets.

He sought help from an internist, a cardiologist, a neurologist and a psychologist, none of whom could find a cause for his problems. Thinking that the patient might have low blood sugar, the psychologist sent him to Lipman and told him to fast before his visit so that the blood tests would be accurate. Ordinarily that would have been sensible advice, but in this instance it led to disaster. Tests in the ambulance found that the patient’s collapse at the wheel had been caused by a blood sugar level of 14 milligrams per deciliter. The normal range is 70 to 110.

On again, off again

Symptoms that come and go are challenging to patient and physician alike. But they are not to be dismissed, because they can signal conditions that are serious, even life-threatening. Here’s a rogue’s gallery of the most significant ones:

Abnormal heart rhythms, such as atrial fibrillation. Many a trip to an emergency room has been for naught as the palpitations suddenly subside in the waiting room. Ambulatory electrocardiographic monitoring is often needed to catch the culprit in the act, because an accurate diagnosis is essential for proper treatment.

Transient ischemic attacks (TIAs), or mini-strokes, caused by vascular disease in the brain, which causes speech and balance problems or facial or limb weakness or numbness. Between attacks, the victim feels fine. Blood thinners can lessen the likelihood of a full-fledged stroke.

Atypical seizure disorders, or isolated, brief episodes of abnormal behavior or visual or auditory hallucinations. Lipman had a patient with a brain tumor whose initial symptom was hearing fragments of classical music.

Assorted rare hormone-producing tumors. One type of adrenal tumor, for instance, can produce surges of adrenaline, resulting in lightheadedness, palpitations and headache.

If it happens to you

As a patient, the most important tool you have is your intimate knowledge of your symptoms. Your goal should be to communicate them to your doctor in as much detail as you can manage. That means:

Leave nothing out, even if you don’t think it’s within the professional purview of the specialist you’re seeing. Lipman once had a patient whose serious pituitary disorder, Cushing’s disease, went undiagnosed for five years because she went to an internist for her diabetes, a cardiologist for her hypertension, an orthopedist for her backache and a dermatologist for her easily bruised skin but never mentioned all four symptoms, highly characteristic of Cushing’s, to any of them.

Describe your symptoms in context. If they change after, say, eating or physical activity, be sure to mention it. A patient scheduled for surgery for a slipped disk in his neck mentioned during his preoperative consultation that movement didn’t make his pain worse but climbing stairs did, a fact he had never shared with his orthopedists. It turned out that his neck was not the problem; the symptoms were caused by coronary artery disease.

Be persistent. Don’t give up if the first doctors you see can’t figure out what ails you. Ill-timed car crash notwithstanding, the accountant’s insistence on seeking new opinions ultimately led to a proper diagnosis and cure.

Tests in a hospital revealed that he had a small, rare tumor on his pancreas that was pumping out huge quantities of insulin, which was causing his blood sugar to plummet. Eight years after surgery to remove it, he remains well and symptom-free.

Copyright 2014. Consumers Union of United States Inc.

For further guidance, go to www.ConsumerReports.org/Health, where more detailed information, including CR’s ratings of prescription drugs, treatments, hospitals and healthy-living products, is available to subscribers.