Regarding your options, let's consider them:
a) flunking out
You've probably put way too much time and effort into this to let yourself flunk out. The only scenario in which this might be the best option is if you're doing this for someone else whom, for whatever reason, you can't confront about the fact that this is not what you want to do.
b) leave of absence
This might be a good option, but you need to think about what you would gain from it. Are you having problems in your personal life that will resolve with time? If so, this is definitely the way to go. You do yourself and your future patients a disservice by attempting to learn this material when you can't really focus on it.
Or do you feel that this is a problem with your ability to learn at this level? If so, the cause could be a learning disability, or it could be that you never really learned how to learn things--you only know how to memorize, and you're so smart that you were able to get all this way without stumbling.
I suspect it's the latter, which is very impressive. However, memorization doesn't work for this kind of material, and taking a leave of absence will solve very little. I don't know enough about how you study to help you, but you may want to visit your campus study skills center (whatever they call it there), and get some help.
What I've learned so far about studying medicine is that it's all very visual. You have to picture in your mind what's happening in the body, instead of just trying to memorize words about it. It's very strange, but when you truly understand the concept, even the details are easy to remember because they follow logically. If you're struggling with that part of it, your weakness may be in logical reasoning rather than study skills. And if you were able just to memorize everything in college rather than reason through to the answer, that may explain your situation. The people at your school can probably help you with this as well.
c) suck it up
I don't think this is the answer either. Figure out the problem, and then ask for help with it.