Watch anyone sight-read something difficult and the same thing happens: the head leaves a neutral position and drifts toward the stand. A pianist leans in over the keys; a cellist's head tips toward the music; a flautist's chin pushes forward over the page. The harder the passage is to read, the further the head travels — and almost no one feels it move.
The notation pulls, the body follows
Reading dense notation is a visual problem before it's a musical one. When the eyes have to work harder — small print, fast passages, an unfamiliar score — the simplest thing the body can do to help is to bring the eyes closer to the page. So the neck extends and the head goes forward. It's efficient for reading and quietly expensive for the neck and shoulders, which now hold the weight of the head out in front of the spine instead of balanced above it.
It tracks the difficulty of the music
The interesting part is how closely the forward drift follows the score. The head sits back in the easy bars and pushes forward exactly where the reading gets hard — the busy passage, the page turn, the modulation. Seen over a whole take, the head position is almost a graph of where the music demanded the most reading. The body is narrating the difficulty in real time.
The head goes forward where the reading gets hard. Lay a session out as a timeline and the head position traces the difficulty of the music almost bar for bar.
Why it stays invisible
Because your eyes are on the page, you never see your own head move; and because it happens gradually, there's no single moment that registers as "now I'm craning." It's the kind of slow drift that a teacher behind the stand spots at a glance and the player, eyes down, never does.
There's nothing to correct here on the page. Just the observation that the forward head isn't a posture flaw so much as a reading response — and that it shows up most exactly where the music is hardest to read.