I've had the same feeling on and off my whole life. I never thought much about it--I guess I thought everyone had it. I believe it's a nerve sensation and nothing more. Next time you go to your doctor you might mention it and see what he/she thinks. In my opinion, if it was something needing immediate attention you'd have symptoms such as weakness, fatigue, lightheadedness, etc. Of course, if you have a history or heart disease or stroke, you should contact your doctor immediately. But what you describe sounds fairly benign to me. Do a search and see what you can find.
Soibhan