Do you not belong in a PhD program if you don't live and breathe your field of study?
In my experience, good primary investigators are always rather unbalanced human beings in one way or another.  If you aren't intensively passionate about something closely connected to the research process, then you can't last, because so much of leading research involves shaping your own agenda.  That said, you can still be doing work in research, even at a Ph.D. level or beyond, without having such independence and drive, but instead being a "super-technician" following somebody else's agenda and leadership.

The scientific ideal holds that every scientist should be of the primary investigator type, and Ph.D. programs are typically designed to select for and cultivate this.  That said, in practice it depends a lot on the group that you are in.  Some professors expect their students to develop their own research agendas very strongly, others are (whether they admit it or even realize it) more looking for good technicians to execute on their grants, and a Ph.D. is more of a byproduct.

We don't really like to admit this as a community, but with the current market structure of academia, we actually need to have the second type of education and people as well.  Look at it from the perspective of simple flux balance analysis: the rate of Ph.D. students entering programs is far higher than the rate at which primary investigators retire or die.  If every Ph.D. student either ultimately ends up as a primary investigator or a "failure," then it means most Ph.D. students are failures.  But I don't think that is actually the case: people who aren't hyper-passionate to the point where it distorts their lives can still succeed just fine in a Ph.D. program and at research, they just are likely to take one of the other tracks besides being a professor or other form of PI.

That said, even if you don't end up going the harrowing road of PI-ship, research work is very hard, and there are a lot of easier and/or more financially rewarding ways to make a living.  To get a Ph.D., you need at least enough passion for the subject to find more value in this difficult and low-paid path than in any of your alternatives.