Light-headedness while jogging

Question
I am 63 and have been jogging at the Y for the last 20 years. I jog to keep my weight down and my heart in shape. I normally run 3 to 4 miles twice a week with an average time of 9.5 mins. per mile.
About a month ago, I jogged 3 miles on a Tuesday. The following Friday I didn't even run a mile before I became light-headed and felt like I was going to lose consciousness; no pain anywhere in my body.
I stopped jogging for about a month and on Tuesday I resumed jogging and couldn't even make a half-mile before the same feelings appeared; once again, no pain.
I've been taking various vitamins on a daily basis for 25 years and I'm a non-smoker.
How could my endurance be so drastically reduced so suddenly??? My heart should be stronger than someone who does not exercise and there are no heart problems in my family. My father is 90 with a healthy heart.
My doctor is convinced I have heart problems as he did not investigate any other areas; no bloodwork, etc. Meanwhile, I've quit jogging and don't see a cardilogist for another three weeks.
Have you ever heard of my symptoms being something other than a heart problem?

Thanks In Advance For Your Reply,
Tom

Answer
Hi Tom
First it does seem strange,but there could be other things that could cause that situation besides heart related.I'm hesitant to elaborate with out asking many more questions to get a better trail of your activity.Would it be possible for you to call me here in albuquerque NM any time so we can go over this information.You can get my number on my web site contact page.I look for to your response and go over this with you.

All the best

John