I am a 48-year old male, and I am beginning to experience a rapid heartrate when I am not active. I have no symptoms during the hours that I am awake and active. For the past six months, I have experienced this problem as much as 4 times per month. I have experienced a rapid heartbeat that wakes me up in the middle of the night. I exercise every day by walking 3-4 miles. I weigh 200 pounds and I am 6 feet tall. My cholesteral levels are around 215 -220, possible lower. My resting heartrate is normally between 76 - 84 beats per minute. I only experience a rapid pulse and noteable heartbeat after I have gone to bed and I awake during my sleep. During these episodes my heartrate is elevated between 120 and 140 beats per minute and it takes anywhere between 5 to 10 minutes for my heartrate to return to normal. This never happens during the hours that I am awake. Could this be from stress or anxiety, or could this signify a medical condition that I should be concerned about?