Running is a traditional symbol of health and vitality in addition to being a means of fleeing potential danger. Thus running could be considered a dream of virility, as well as fear.
Usually, in a dream of running in which fear is the dominant emotion, you will find that you can either run all night and successfully escape the danger (albeit with a serious emotional drain), or you find that you continue to falter and stumble, making the object of your fear even more terrifying. In the latter case, try to relate the dream situation to a situation in your life where you are feeling incredible pressure. Sometimes a simple change of perception can solve the problem.