You practice your music incessantly. Perhaps you even "role play" your performance in preparation for the real thing. Perhaps you worry about any lapses in memory of your lyrics that you might have. This is the common ailment of "perfectionism" in the emerging artist and we all encounter it and need to combat it on a regular basis. This is not to say that regular "practice" should be avoided or that performance preparation should be eschewed. Far from it.
Rather, it is what we "practice" that should be looked at. Specifically, I find that when watching emerging artists, if they stumble, the likely cause is a failure of focus, namely focusing on "being present in the moment" rather than focusing on "how they appear to look" to the audience. It is self-consciousness that interferes with a performance. When we become self-counscious, we are no longer paying proper attention to either the song we are performing nor, by extension, the audience we are performing for. The internal conversation becomes "self-centered", not "audience-centered".
Combating this pernicious tendency requires something many people have a hard time doing: subordinating their own ego and simply acting in a way that is as natural as walking down a street. Half the battle is admittedly feeling self-confident enough about your musical technique, whether instrumental, vocal or both, to be able to conduct your performance without a specific conscious focus on it. It is the quality of being "loose" and relaxed while performing. I think the other half of the equation is simply being "comfortable in your own skin" so that if you do make a musical stumble that would be apparent to you, that you are comfortable enough not to react to it or, if you do react, do so with self-deprecating laughter at yourself. Remember, the audience wants you, as the performer, to "succeed", to seem, for all outward appearances, to really enjoy yourself being on stage. That is the real goal and personal enjoyment and self-consciousness simply don't go together when performing.
Food for thought.
Yours in DADGAD.