that depends by your definition of break (how long) and when you have your interview (within days? Weeks? Months?)
In general an appropriate break would not be an issue. However, there is another question you should ask yourself. Why do you feel exhausted?
It is likely you have overdone with the preparation. Which could mean you have not prepared a correct plan for your interview.
One of the most important things in consulting preparation is to organize an appropriate and balanced calendar for your preparation. Doing cases is like going to the gym or learning a language: you cannot expect to be in perfect shape or have prefect knowledge in days or even weeks. Rather, you need a predefined program, from the moment you start until the moment you stop.
So, to answer your question: yes, feel free to take an (appropriate) break, but be sure you have a clear, sustainable program from when you start again, that you can follow from the day you start till your final round, in order to avoid to burn out again.