I've been reading, and one major mental thing to deal with is all the other people, that are either slow, or rushing past, or crying and quitting and the like.
That sounds like an amazing make or break (fight or flight) moment for your adrenaline! Something I would love to experience!
I'm considering doing it in Aus, it is on in September and cost $110. Being a student I am very put off by the price, I'll see if I can find sponsorship..... off my mummy! lol.