I am a 55 year old male. In good physical condition--gym 3 days a week, run 3.5 miles 3 times a week. Have run for 35 years. I was out running today and my heart rate was my normal exercising rate of 146-156 bpm. On two occasions I had a light-headed dizzy feeling for 3-4 seconds. I looked down at my heart rate monitor and one of those times my heart rate was 220 and the other time it was 226. It only lasted 3-5 seconds but I was concerned. I had a series of episodes 5-6 years ago, went to a cardiologist. Found out it was because I had been fasting for 36 hours and when I ate it drove up my blood sugar. Does anyone know what this could be.