I am woken from sleep at times with racing erratic heart beats. It is terrifying I feel like I am having some kind of heart problem. I have to get up. This can last from few minutes to 20 minutes or longer. I had chest discomfort on my left side which also goes up the left side of my neck. When I took my blood pressure this last occasion, the monitor showed afterwards my pulse rate was 104 and BP 138/67. I am on Bisoprolol 5mg. Can you please tell me what causes the racing heart episodes.