I understand your problem, I've had the same and it is caused by anxiety, which is caused by stress. Try taking up some kind of relaxation technique such as progressive relaxation, which is a form of Yoga. Its not a miracle cure but it will cure the problem over a period of time and restore your self confidence. This sort of problem happens when you become too stressed for whatever reason. Stress creeps up on you over a long period of time and causes all kinds of problems. The solution is to reduce your stress levels and then normal service will be resumed.