Sleep deprivation, steady stream of yelling correcting your every movement, standing/walking all day long, short periods of rest, hours of exercise/training and transforming yourself into your best version. Its really incredible you should experience it for yourself.
I personally suggest you take some basic swimming classes on your own before you attempt being taught how to in the Marine Corps. Trust me its not a swimming course you want to take lightly. Yes it will cause you not to graduate.
Study on your weaknesses and grab ASVAB Study Guide 2014: ASVAB Test Prep with Practice Questions if you haven’t already.