It is a subjective feeling associated with the insistent desire to sing!
Like that of a "tight-rope walker" as he steps on the wire;
Like that of the swimmer as he ceases efforts and trusts the support of the water;
Like that of the diver, the moment before beginning his plunge;
Like that of the listener who hears a mysterious sound in the quiet of the night;
Like that of the sharpshooter the instant before he pulls the trigger;
Like that of the archer the instant before he releases the arrow;
Like that of the expert whistler just before he makes a sound;
Like that of the juggler at the beginning of his act;
Like that of the dancer as he rises on his toe;
Like that of the orchestra conductor, with his baton poised poised in the air;
Like that of the orator as he opens his lips before the waiting audience:
All these acts demand objectively, a potent vitality, conscious, accurate control of energy, and complete knowledge of the thing attempted.
When you are sentient from head to foot and know your song, then you are ready to sing.