Question

An older woman is gardening in the direct sun for three hours without any rest. she suddenly feels weak and dizzy before she faints. she is taken to an emergency room where the doctor suspects she is suffering from dehydration. this is a common problem in older people because:

Answer 1

decreased thirst reflex with age, or if they suffer from dementia or physical immobility. 

Answer 2

He no longer feels the need to hydrate, drink water.
It has less perception "of thirst".