At the other end, there is a near death experience. Somewhere in the middle is a cross over point. Some people find that facing an audience of thousands is nothing, but performing before a small group turns them into jelly. Others find an audience of friends more intimidating than strangers. Each performer has a unique profile of bugaboos.
Preparation is absolutely necessary.
Not knowing is a cause of anxiety. Practice by video or audio recording yourself which helps to visualize performance and to develop muscle memory. Researchers have confirmed that use of video tape in preparation for public speaking or singing reduces anxiety and improves performance. Develop an inconspicuous personal relaxation ritual. Singers, musicians and dancers can often do this behind the scenes but presenters are usually on the stage before their performance and would look a bit odd doing tai chi, yoga or standing on their head.