The Nuances Of Creative Passion
Dr. Scott Barry Kaufman on explores the different kinds of passion -- healthy and not-so-healthy -- for a creative pursuit, from a Reena Jana interview with him on CreativityPost.com (originally posted at frogdesign):

Can you share a condensed definition of the psychology world's definition of "passion"?
Passion is the energy that can fuel a project, or a task. It has a similar role to inspiration. When we engage in something we are passionate about, we feel free from external constraints and in control. Time recedes into the background, and we feel allowed to engage in flow. Research has shown that flow correlates directly with passion.

Psychologists have been studying "passion" for years in the lab. But only recently have we been conceptualizing it. We understand lots of different conditions of passion, especially what is known as harmonious passion, or positive passion. It's actually very important to distinguish between different types of passion. Sometimes we encounter wolves in passion's clothing--otherwise known as obsession. Robert Vallerand has done the large majority of research in distinguishing obsessive passion from harmonious passion.

So there are two types of passion?
At least two, with very distinct fingerprints. Interestingly, in studies, people who self-report either harmonious or obsessive passion perceive their drive is "passion," without qualifying it. They value their sense of passion highly, but that is where the similarities end. With obsessive passion, unlike harmonious passion, a person feels controlled by work, as if not in control. Harmoniously passionate people can engage in work in an intense way, which they self-report as "concentration." This feeling of being able to concentrate at work correlates more with harmonious passion than obsessive passion. The key difference is the extent to which a person is in control of his or her environment. People who experience harmonious passion feel more intrinsically motivated.