My PMP exam was largely as I expected - the nature of questions, the distribution, etc.
My PMI-ACP however, threw me off balance. The types of questions - were so very confusing, and I was not able to second guess which aspect they were trying to test.
I made a conscious decision halfway through the exam to keep calm no matter what.
Nerves can spoil focus of even the most knowledgeable people, and I didn't want to find out what they could do to me!
I would say - practice until you are confident, and are really comfortable with the concepts. Then mentally prepare yourself to feel out of your depth during the actual exam. Take a deep breath, and just do your best.
USE THE REVIEW OPTION!
This is a great functionality the exam offers you - very often one can miss some detail about a question on the second read, which makes it clear what the answer is.
All of that - and all the best!