It's not every day you hear about a successful emergency room doctor giving up his practice to run an Internet company. But back when the Web was new to most people, Dr. Ash Nashed found it to be a useful tool for teaching med students, something he was also doing at the time. He was so passionate about this new technology that he gradually scaled back his hours at the hospital, eventually putting in only one shift a week so he could work full time on The HealthCentral Network, one of the first medical websites. Later, he founded Adiant, a multimillion-dollar digital media firm that provides advertising solutions for publishers and advertisers. Here's his advice on how to know if it's time to make a radical career change.

The career shift will meet some unmet personal or professional need.

In Nashed's case, working on The HealthCentral Network provided him with a creative outlet the ER and classroom didn't provide. Other voids a career change could fill: Financial stability, if you're willing to move out of self-employment into a 9 to 5 job with a regular paycheck every two weeks; more or less interaction with people, depending on whether you're an introvert or extrovert; as well as more or less travel, depending on how much you want to see other places or be at home.

You can bring a unique perspective to an industry.

When Nashed started The HealthCentral Network a lot of people were getting involved in the online medical information space, but very few could say they were both physicians and educators. "It's a definite plus if you're looking to make a career change," he says. "You can leverage your own unique experience and add something to that ecosystem that might not be there."

Your family supports you.

To make a radical change in your life, you need the people closest to you in your corner. "Sometimes people don't see the future opportunity in what you're doing, but having people behind you will make it much more possible for you to succeed," he says. "If you have people who are not supportive, it just stacks the deck against you even more than natural probability of success."

You're onto something brand-new and golden.

Nashed didn't have any experience with the marketing industry or digital media, but he entered the space at a time when no one else did either, because online media was a whole new thing. "If I had stepped into digital media and digital marketing [today when] people have now had a 15-year runway to learn and become familiar, I think it would be much harder for someone like myself to succeed in an industry that was so different from where I came from," he says.