Isn't this the bodies way of coping with fear and/or excitemnt, you describe what I feel every time I approach the airfield, as either P1 or Pax, but as soon as the pre-flight is started its all gone and the reality of flying takes its place, I then get that same feeling walking away from the Heli after shutdown and post-flight checks have been done, I dont think you are out of the ordinary in what you feels!