What Causes Sudden Increase In The Heart Beat Rate?

. I also have been awakened by rapid heart rate and am very scared. I am a 39 year male. I sleep fine and only when I am awakening do I find myself succesptable to tachycardia. This happens about 3 times per week. Example, I go to bed at 1130pm and then I sleep very well until 0300am, at which I awaken. While I am in the asleep/awake mode, if I move, turn over in bed, I go into tachycardia for about 5-15 minutes. It feels like my heart is beating out of my chest. I have called 911 twice only to turn them away as to the time they get here I feel fine. The only thing is as I am awakening I can feel my heart beating and it is slightly iregular. During the day it is not. I do feel the occasional irregular beat though. I had a cardiolyte stress test and It came back fine. The cardiologist told me I must have an electrical problem and gave me an event monitor. I will keep this board posted