You've heard it all: Think about your audience more than yourself, imagine your audience loves you, imagine your audience in their under-roos, take a beta-blocker, over-prepare, meditate, levitate, just do it, and my favorite; all great performers have stage fright. But, come on. If you have real stage fright, none of this matters--not of this advice even comes close to helping.
I'm not talking about feeling jittery, or excited, I'm talking, excrement/vomit/horrible-headache, why-am-I-doing-this, kind of stage fright. That is a real monster, and here is the cure.
Stop performing. That's right. Just end your career now. No one cares. The world doesn't need another version of whatever you're about to do. Do not quit your day job, and immediately stop practicing. Don't even think about singing in the shower, and definitely knock off that annoying habit of humming when your happy. In fact, make fun of anyone who even attempts to create some form of human whimsy.
Make sure you let everyone around you know about the horrible, current state of the arts. Picture yourself in 10, 20, 30 years having absolutely no more to do with this performance nonesense. Instead, binge watch all the shows you fancy, and many that you don't. Block yourself off from all human contact, except a couple of people who are equally bent on dissing the world. Drink yourself to sleep each night, cursing your very existence.
Imagine at the end of this worthless existence, you keel over from a heart attack, and just as your pathetic life is trickling out of you, you wish: I wish I would have kept singing. I had talent, and had something to say.
Roll back the tape to right now. You are still alive. You love, (okay, sometimes just like) to sing, and you have good days and bad days. Beverly Sills reportedly only felt that her voice was in full working order in only six of her thousands of performances. Seriously, does it even matter?
Yes. It does matter. Someone in the audience needs to hear what you have to say, (even if that means making fun of your terrible performance to make themselves feel better.)
Albert Ellis, the Grandfather of Cognitive Behavior Therapy, has a fabulous exercise. Imagine the absolute worst that could happen to you during your performance. Let's say you forget the words and crack a bunch of notes. Now let's say that you soil your dress or pants and projectile vomit on your leading man. Now let's say that you fall off stage and kill someone in the front row, and that sparks a chain of gun violence not seen since WWI. Sounds pretty bad, but it gets worse. The theater catches fire, and people run into the streets catching the entire city on fire. An underground arsenal of nukes explodes and the entire continent is wiped off the map. All of the fish in the seven seas die, and soon, every living thing on earth is dead.
The last living amoeba exclaims: I wish I had several hundreds of millions of years to develop, so I could share the miracle of the human voice with others on the planet. You are a miracle, and so is your voice. Do your best, and thank you for having the courage to try. As an audience member, I need music, I need your singing, I need your message, I need your art, and so do 7.something billion other people. Boca Lupo! (By the way, that means Mouth of the Wolf. The audience is the wolf's mouth open to devour you. You, the performer say, to the wolf, "F-You, wolf, I'm a human miracle, and this is my song.") P.S. It also helps to practice in front of small loving audiences before you take serious risks. P.S.S. Mindfulness Meditation helps to calm down your brain that's being flooded with cortisol, and adrenaline while your prefrontal cortices are shutting down. Jump up and down until you're winded. Now sing your songs again. Repeat, until you get used to singing through stress. If this doesn't help, go back to step one and just give up.