What you simply must understand is that admissions committees are well aware of one simple fact in life:
**** happens.
Would you like to know the reason med school hopefuls are required to take ALL of these sciences, AND the daunting MCAT, AND somehow find time in between to have patient contact/research/volunteering?? It's so they can shape a solid picture of who their applicants are without having to rely solely on how academics paints the individual.
I understand that most premeds are under the impression that life revolves around their applications. But, much to their utter shock, it does not. People get sick, family members die, relationships fade, semesters suck. What you have to do is make those semesters work FOR you; not as your antitheses.
You have SO many other opportunities to come across as a shining example of a future physician. And, if you're worried that ONE semester of sub-par grades is going to kill you, then you have MUCH more to worry about than a couple of Bs.
Look at your overall self. If you were an admissions member, what would YOU see in your applications? Would you be fixated on one bad semester (out of the COUNTLESS semesters we all endure) and discount all of the amazing EC's, the strong MCAT, and the upwards trend? No. That would be absurd.
Let me tell you something: my transcript boasts about 4 Cs that are sprinkled intermittently throughout the A's and B's during my undergraduate career. Currently (being late in the decision to go to medical school), I'm in a post-baccalaureate program to complete the pre-reqs. And, the last few weeks of this semester, I have to work my ASS off to get A's. Right now? B City.
So, if an admissions member asks me about certain grades here or there, I'm going to look them right in the face and tell them the truth: I did my best in class, and I am fully aware that my grades do NOT define my intellectual capabilities. I would then advise them to look at my over all application and see that I was also an athlete, a researcher, a volunteer, and a student leader.
Don't get so hung up in grades. Sometimes, you falter. You're going to. You're human. And guess what? Doctors falter to. What separates those who get accepted from those who don't is the confidence to tell medical schools that you're more than a number, and to PROVE to them by any means necessary that's the case.