How to musicians manage to remember how to play/sing

[DuckyMcDuck]

When they're obviously off their faces on something?

Watching YouTube videos and Robert Plant singing Kashmir and Stairway.... totally off his face and yet he's word perfect. Jimmy Page playing so beautifully and yet smashed.

Muscle memory for the guitar/ instrument. If you play something often enough your hands just do it! God knows how they remember the words tho!
I play guitar but really struggle to sing at the same time

Muscle memory.

I'm currently having singing lessons and it's a lot of practice and it almost becomes second nature.

I cant multitask either! Yay its not just me!