Hypnosis can be helpful for anxiety before performances. Many people experience normal anxiety when having to perform in front of an audience, so hypnosis can be helpful in these normal situations (Hammond, 2010).
However, if you have a more severe performance anxiety, to the point where you absolutely can't perform in front of people without having a panic attack, then you may have an anxiety disorder, such as stage fright (performance anxiety), which is a subtype of social anxiety disorder (social phobia). For anxiety disorders such as stage fright, hypnosis alone will not eradicate the anxiety- rather, hypnosis can be an add-on treatment to a primary treatment (like CBT- cognitive behavioral therapy), but not a primary treatment.
Hypnosis in the treatment of anxiety- and stress-related disorders. Hammond DC. Expert Rev Neurother. 2010 Feb;10(2):263-73.