Writing this once so I can stop repeating it across threads. It is about hydration and electrolytes, and it is deliberately narrow — everything I am not confident about is marked as such.
What is actually established
Two things drive this: people drink less because drinking makes them feel full, and they restrict salt at the same time as calories without noticing. The result reads as fatigue, headache, cramp and light-headedness on standing, all of which get blamed on the drug. Fluid plus sodium fixes most of it within a day, which is also how you can tell that is what it was.
The condition it depends on
The kidney-stone risk is the reason to take it seriously rather than just uncomfortable. Concentrated urine over months is a stone-forming condition.
The practical version
The test is quick: add fluid and salt for two days and see whether the symptom goes. If it does not, it was not hydration and it is worth a panel.
What I am not sure about
What I am trying to establish is why hydration goes wrong on this specifically, given that nobody is telling us to drink less. I would rather have one careful answer than five confident ones.
— NurseKim_ATL · corrections welcome and will be edited into this post with credit