Dear Dr. Gott: My son, who is 15, has been suffering for the last year with a debilitating illness. His symptoms are dizziness, tunnel vision, which turns into total blackness, severe headaches and feelings of blacking out.

He will have to stand in one place with his hands against the wall for support until his vision returns. He has seen a neurologist and a cardiologist.

The cardiologist suggested syncope (fainting), and the neurologist saw nothing on an MRI.

My son is desperate to find out what is wrong with him. After a little online research of our own, we are thinking orthostatic intolerance. His symptoms occur upon standing. What do you think?

Reply: Some children and adolescents experience pre-syncope, a feeling they are about to faint. They may complain of dizziness and a feeling that the room is spinning. There may be episodes with adequate time to slump to the floor or sit in a chair, while at other times a person may fall to the floor without warning.

The feeling is frightening for an adult and overwhelming for a child, so I can understand his anxiety.

An irregular heartbeat can be a trigger. When the condition occurs, the ventricles don't have adequate time to fill with blood before that blood is automatically pumped throughout the body. The body reacts to the decreased blood supply by shutting down, causing fainting to occur.

Abnormalities in the structure of the heart can also cause near or true syncope. An outflow obstruction restricts the flow of blood out of the left ventricle of the heart. Certain cardiac conditions, such as aortic stenosis or myocarditis, will diminish the flow of blood through the aorta, causing symptoms of syncope.

A drop in blood pressure on standing or when a child has been standing for an extended period is known as orthostatic hypotension.

Blood pools in the legs, preventing it from returning to the heart in adequate supplies. Simply put, when the heart doesn't get adequate blood in, it can't pump adequate blood out. Syncope results.

The vagus nerve is essential for the function of numerous body parts. When stimulated by conditions such as stress or pain, blood vessels dilate.

This leads to a slower heart rate in susceptible people, resulting in syncope. Still other conditions, such as inner-ear disorders, low blood sugar, head injury and voluntarily holding one's breath can create similar symptoms.

A common thread to some syncopal conditions is an inadequate supply of blood to and from the heart. Your son should be seen by a cardiologist who specialises in paediatrics.

While I understand he may not feel comfortable in a paediatric setting, I believe he will be better served there. Based on his history, he may require lab work, a tilt-table test, an echocardiogram or other appropriate testing before an accurate diagnosis can be made.

Because I mentioned ear infections as a possible cause, I am sending you a copy of my Health Report "Ear Infections and Disorders".

Other readers who would like a copy should send a self-addressed, stamped, number 10 envelope and $2 to Newsletter, PO Box 167, Wickliffe, Ohio 44092. Be sure to mention the title.

Dr. Gott is a retired physician and the author of "Dr. Gott's No Flour, No Sugar Diet" and "Dr. Gott's No Flour, No Sugar Cookbook". Contact him c/o United Media, 200 Madison Avenue, fourth floor, New York, New York 10016.