I am old enough to recall a time when we didn't call it 'hydration' we just called it 'drinking water.' I'm not saying that the hydration craze is totally without merit, but it seems that somewhere along the line the word went out of control. I read somewhere that Timothy Noakes has documented quite a few cases of over-hydration (water on the brain maybe) where people had been advised to drink way too much water for running.
It's a similar case to "road rage." We always had discourteous driving, but around the mid 90's someone coined the clever alliterative "road rage" and it became a thing unto itself. Laws were passed, police squads were formed, etc.
The interplay between language and behavior is interesting...