I can’t sing and I get very nervous if I have to speak so I am not very much help. But I did read an article once how taking deep belly breaths (even if they sound funny) help because in a fight/flight situation (which the body will construe this as), the body resorts to short, shallow, fast breaths. I assume that the longer, slower breaths alert the body that the crisis is over and relaxes the body accordingly. I am sure there is a better medical explanation out there about how it works, but there is no harm in trying it.