The physical and mental changes produced by fear are not all unhelpful to a singer, provided they're controlled and used to advantage.
The effect of adrenaline in the bloodstream produces what's known as " the alarm reaction", which is nature's way of responding immediately to perceived danger.
Positive elements of this reaction include heightened awareness and energy, and increased acuteness of hearing. These are useful qualities to bring to performance.
Adrenaline can also produce an increase of focus and clarity in performance, adding to a singer's "presence". Presence is the quality which makes one performer more watchable than another. It's as indefinable as sex appeal but just as instantly recognisable.
