The mind is made up of two parts; the conscious mind and the sub-conscious mind. The conscious mind is the rational, discerning portion of the mind and the sub-conscious portion is the emotional, protective mind. The protective portion of the mind will protect you against everything, real or imagined. Once the sub-conscious mind identifies a threat it goes into the "fight, flight, and freeze response". Once the sub-conscious mind perceives a threat, it starts to pour adrenaline into the body causing the body to begin to shake. Blood is diverted to the muscles in preparation for defending itself. The body begins to sweat profusely in order to cool itself down as it struggles with whatever is threatening it. As the sub-conscious mind is really in control, the sub-conscious mind will only release a person from this mode once the threat has been removed.
Sometimes the sub-conscious mind is conditioned to perceive threat incorrectly and stage fright is a perfect example of this. Imagine walking out onto a stage. As you walk up to the podium time seems to slow down and your body feels like lead. In front of you are hundreds of people staring at you intently. You try to open your mouth to say something but your whole body has frozen. You realize your knees are shaking and this shaking starts to spread to the rest of your body. The sweat starts to pour down your forehead and you are powerless to do anything. Your body has been slammed into the "fight, flight, and freeze response".
Using hypnosis, it's easy to rapidly re-condition the sub-conscious mind so that it no longer perceives an audience as a threat. It's easy to train the sub-conscious mind to enjoy public speaking.