Hi Ben25,
I would go with, no, your personal statement is not the correct place to talk about your C in physics. I say this for two reasons. First, I think personal statements are best used to highlight your motivations for med school etc. You want yours to be positive and not bring attention to something negative in your application. If you mention your grade in your PS, I think that's exactly what it will do, bring unwanted attention to it. Second, one C is not the end of the world and assuming your other grades were decent your GPA will show you are smart enough to do well in med school courses, which is all the adcoms really want to know. If you are that worried about your grade, it would be more appropriate to explain this in secondaries or an interview, if you need to explain it at all. Maybe others can weight in on this issue as well? Good luck with your applications, wishing the best!