First, Breathe. You are going to make it through this. Of course it's tough. It has to be, because one day you will be interpreting your assessments to determine if what you see is relevant to the patient's outcome. Your medical field experience will help you in time. Whether it is by time management, speaking with your colleagues, or judgement calls.
Keep in mind that you are in a different place than your fellow classmates. You study differently and your decision to get this degree was probably more thought out than several of those that need to repeat.
Critical thinking takes practice, and that is why the questions are worded the way they are. Don't think of it as a way to point out your shortcomings. Instead try to see how the questions help to mold how you think. Be sure to review your exams, and you will slap your forehead because you TOTALLY knew that answer, but read it wrong!
My advice to you is to read. Read until you have got it! If you are tired, take a break or sleep, and then pick up where you got lost. I would even review the relevant chapters in Saunders after reading. It will help to guide you in what they want you to see.
Good luck and hang in there! Don't let the chatter of how horrible it will be distract you. Your experience will be your own, and will not be the same as others.