The percentage/grade for passing is very variable from school to school as are the consequences for failing a test or a course. For the medical school that I attended, the raw score for passing was set by the individual test and normalized so that the percentage always changed based on the class performance. This generally helped the people who were at the bottom and slightly penalized the people at the top unless you were well above the mean. If you failed a test, you were OK as long as you pulled up and passed the course. If you failed a course, you could remediate in the summer. If you failed more than two courses, you could be dismissed or dropped back a year depending on what the promotion committee decided.
The medical school where I did residency, set a specific percentage for passing, and that didn't change. You may have to remediate a course or remediate a test depending on what you failed. Very few people ended up repeating an entire year of medical school (perhaps 1 or 2 out of more than 150).
The interesting thing is that people who failed a course or two and re-mediated and even those who ended up dropping back a year usually rocked on boards and ended up in great residency programs (not in Derm or Optho) but solid programs in just about everything else. Of the people at my school that ended up with a rocky start, a overwhelming majority ended up doing pretty well after they figured out what they needed to do and got it done.
The thing to realize is that you have to figure out your problems; take care of them; and pass your coursework. If you are failing in a couple of courses, then you need to get some serious assistance before you fail the course. If something (illness, personal problems, financial problems etc) is preventing you from getting your work done, take a LOA and work out the problem so that you can come back and devote your full attention to your studies before you get to the point that some academic action has to be taken against you.