OK, Been there, done that...sort of. About 30 years ago I had been in this particular band for about a year. We were doing were doing quite well, locally. Nice following, good crowds, played the nicer clubs in town, etc, etc.
We were learing a new song called Jackie Blue, by the Ozark Mountain Daredevils (at least I think it was them). I sang LEAD on this song. I sang lead on about four others, but we had a "lead" singer for most of the others. He insisted we do the song one night. I told him I wasn't comfortable with the chord changes AND singing it, yet. I wanted one more day to practice.
But NOoooo! He insisted. The other guys gave in. We start the song. The intro goes by, I start to sing and hit the WRONG CHORD!!!

Instant Panic attack!!

But I kept my cool and quickly started faking singin! Moving my lips but no sound. I looked like my microphone had died. I even pretended to tap on it and no sound came out.
We asked for a minute, played with the mic cord. it "started working again" and we went on to the next song. He tried it again the next set. I got it right that time!

Of course , that was after taking my guitar back into the dressing room and practicing the start of it over and over for 20 minutes!
So, moral of the story... no sweat! I does happen to people who do this regularly. Just a mental blank once in a while.
Same band, a few months later.....we had 50 songs on our list. Just before going back on stage after a break some girl asked me how I remembered all the songs.
I said,"geez, I don't know, I just do." First song out of the chute, I start the singing. My brain takes a break,

I start to think "WHAT ARE THE FIRST WORDS!!??", I just stood back from the mic (much to the worry of the other guys in the band. They thought something was wrong) I tried to make my mind a blank and not think about anything. I step back up to the mic and open my mouth...out come the words.
Like LCjones said "when you become one with the song, you are the song. you no longer "think" about the song or the music. it just comes naturally"
Keep practicing, it will all start coming together in little time and will be natural to you.
Just enjoy what you're doing, that's the key!
