I was a pre-med turned pre-opt. I had considered optometry before, then decided that I wanted to go to med school and hopefully go on to ob-gyn. About midway through sophomore year (before I had taken the MCAT), I started thinking optometry again. GPA wasn't a problem, but I did start thinking about what I wanted my life to be like when I was out of school. There are medical professions that allow a 9-5 work schedule, but ob-gyn is not one of them. I thought about it a lot, observed some ODs, and decided to pursue optometry instead. Of course lifestyle isn't the only reason I decided to go the optometry route, but it is a valid one. It wasn't a hard transition since the pre-reqs are more or less the same.
Edit: I think there are actually a LOT of us out there with similar stories....