One of the fundamentals of singing is learning how to sing higher. Of course, as we do so we certainly do not want to stretch our necks up like a turtle. Nor do we want to squish our necks down and push and press the tone.
If the closer muscle is doing its job, and the stretcher muscle has been freed and exercised so as to stretch, then our heads can remain level as we trust the vocal muscles to do their jobs. Just like a walk up the steps, as we ascend the scale, it will feel like we are stepping up a staircase backwards becoming taller, lighter, thinner, smaller, and a bit more energetic. The notes seem to have less weight as we sing higher.
How do we walk up the steps? The way this is accomplished is that for each and every step up the scale, there is less length, width, and depth of vocal cords vibrating. Our vocal cords or the steps are literally getting smaller. We then have moving muscle (like in our legs) and moving air (energy flowing) to lift us up the steps, one after the other!