It is often said that “you’re already severely dehydrated by the time you feel thirsty”. But it’s not true for most people, who feel thirsty with 1% dehydration. More severe dehydration might produce loss of tears, dry mouth, changes in urine, certain changes in blood pressure and with posture, dizziness, etc.
I use the phrase “Nintendo medicine” to diagnose people based on minimal information (which shows my age). But based on the OP I would (1) ask about stresses, medications and caffeine intake (2) screen for diabetes, thyroid and electrolyte profile (3) check sitting and standing blood pressures and pulse.
I’d screen for anemia too, but this is done through physical exam (does the red things under the eyes and tongue look pale?).
As you got older, did you notice your body lost the ability to tell you when it is thirsty?
I know people lose their ability to regulate temperature with age. Like I can go outside in winter w/o a coat to get something from my car. My dad could do that at my age, but can’t do it now.
I mean everything fails in the body with age, so I guess its natural to assume that water regulation also fails.
As I have gotten older, I have taken to somewhat restricting my liquid intake in the evenings, to reduce the need to get up and pee in the night (it doesn’t work). I suppose that, as I get even older, this could result in not getting adequate hydration.