Change happens on a cellular level. The gist is this: we all get hooked on hormones. For example, if you are used to being stressed all the time, your cells not only adjust to the high levels of cortisol (that’s the “stress hormone”) in your system, but you actually begin to like it, and then need it.
In short: you get “addicted”.
Ever feel weird while or shortly after relaxing, after experiencing a lot of stress? It’s because you’re on withdrawal; your downtime has literally become your rehab.
The same thing happens when you workout a lot: you get used to working out, your body produces and gets used to “consuming” dopamine and serotonin, and then proceeds to whine about not having those hormones when the workouts stop.
Personally, I've always had a hard time taking a real vacation (to the complaints of my wife). Going from high stress/high stimulation environment to peace and quiet was unsettling.
I was programmed for stress...