The root cause of your FEAR in performing, public speaking, and writing is the LACK of planning, organization, and preparation.
All these point to the art of communicating. Contrary to what most people think, for example, public speaking is not just confined to the stage. Whenever or wherever you have "an audience" whether it is for a few or a couple of people, you are actually on "spotlight" and expected to articulate your thoughts well. The same principle underlies all three... generating ideas, organizing ideas, and delivery.
PUBLIC SPEAKING 101-103
MUSICAL THEATER AND THE SCIENCE OF THE STAGE