It's a good idea to bring any symptoms related to exercise to the attention of your doctor, but in a quarter to a third of people, the dizziness and other symptoms in the midst of working out may be due to low blood sugar brought about by exertion.
Walter Johnston's athletic passion is running, but over the last five years he noticed some strange symptoms that threatened to put in on the sidelines.
"As I ran, I would start to see spots in front of my eye, then they would come together and I would have one big hole in my vision," explains Walter. "If I kept on running I would eventually start to tilt, to lean to one side."
It wasn't his heart or a stroke. It was his blood sugar.
When Walter went to see the doctor, his treadmill test was not perfect on his first go-'round. His sugar was far below normal and he was having exercise induced hypoglycemia - a very low blood sugar that results from working out.
"It seems to come about when somebody eats something sweet prior to exercise. Very classically, it happens about ten to twenty seconds into exercise," Beth Glace, a sports nutritionist, said.
Walter's symptoms happened if he ate carbohydrates within a couple of hours of a run. Other symptoms can include lightheadedness, hunger and cold sweats.
When you eat something sweet before exercise, insulin enters the blood to keep your sugar levels stable. Some people are super sensitive to insulin, which can drop the blood sugar to very low levels with exercise.
His first treadmill test showed the low sugar just when his symptoms started. A second test, showed his sugar level was fine.
The solution was pretty simple, he stopped eating at least four hours before a run.
"Since I've used that formula, I haven't had a single episode of the hypoglycemia, which is wonderful," says Walter.
Hypoglycemia can be a dangerous problem for runners who exercise close to busy traffic lanes or for cyclists who depend even more on balance.
Beth Glace says it's ok to use sports drinks or other carbohydrates after the start of an exercise.
Still, you should always check with your doctor to rule out heart or blood vessel problems.