People who love their job (or seem to project that aura) simply bleed exuberance. You see it in their gait. You heat it in their voice. You feel the power through their gaze.
While such dynamism in life lends to a sense of fulfilment and optimism, it too forms the classic U-shape dose-dependent relationship; A little is good, some is better, more is detrimental.
Those living at the high end of the spectrum are particularly in danger. Their passion feeds their minds and soul, and they in turn keep asking for more - ignoring the pleas of the body to tone it down a little. They lose sleep, work harder, and neglect family, and they love it. The eventual physical burnout is swift and merciless.
Make sure to keep your passion within its bounds. How do you know you're pushing it too far? Your stomach will speak for itself.