As with any fear, the fear of public speaking can take on a physiological form. There are ways that these symptoms and feelings can be minimised, and attending Train The Trainer Courses like the ones from the College of Public Speaking can be a great place to start.
When a potentially threatening stimulus is presented, fear and anxiety trigger the autonomic nervous system to arise in response to the arousal of this system. The body prepares for battle when it is confronted with a real threat or even one that is perceived. During times of hyperarousal, we experience fear as an emotional experience that interferes with our ability to present ourselves in a confident and comfortable manner in front of audiences. It can even prevent us from pursuing public speaking opportunities in the first place.
Those who are prone to feeling anxious find it harder to master their anxiety and thus overcome their fear of public speaking if they are predisposed to feeling anxious and will choose instead to avoid public speaking altogether. Others experience anxiety only in public speaking situations, but the physiological signs of the fear they experience as they plan, prepare and build up to their public speaking will be very similar if not identical to those who experience anxiety related to other situations.
In any situation where fear is holding you back, it is always best to try and find ways that you can overcome this fear in a controlled environment.