Hi wonder if anyone can help. I am getting very frustrated and worried. I have just been for an hours run my heart rate shoots to 190 very quickly without me even being very much out of breath, I was running along quite happily singing to my ipod and my heart rate was still around 190. After running for a couple of miles I was on the flat and then looking at my monitor and my heart rate was 46, I thought maybe my monitor had stopped working but then as I went up hill I had a funny turn which I have regularly whilst exercising and my heart feels like its gonna pop out of my body my legs go very very weak and i go very dizzy, my heart rate went to 228, after walking and breathing deeply it then returned to about 186. Not really sure what my resting heart rate is but I have now been sat here on computer for about an hour an my heart rate is fluttering between 86 -96 bpm. After I have finished exercising I feel very tired and could actually nod off to sleep. I am of average fitness I work out around 3-4 times a week for an hour at a time. Is there cause for concern.