I sort of regret the shower/range-going-south comment as it's misleading. If my lips are a bit stiff due to dryness etc., my general playing is rubbish but I can squeak out something close to a G above high C. On a fresh, relaxed lip, high C is pretty comfortable. I'm not working to extend this range, just strengthen the range I currently have. Pretty sure a couple of notes above that will turn up of thir own accord when they're ready
And "equilibrium" is the right word, though many people (including too many engineers) would misunderstand it. Strictly speaking, a stable resonating system is a perfect example of what we call "dynamic equilibrium": stuff is in constant motion, but repeating the same cyclic sequence.