Moar events - now posted in the right place! :D;;
What will happen is: The characters will have either really cracky dreams, nightmares, or, er, wet dreams. They'll be very vivid, and once they begin, it'll be hard to wake whoever's having them for a while.
It's not mandatory, so you can either not play the event at all, or have your chara dream all three different types of dreams during the time the event lasts!
Once a chara has had one of the dreams, though, they won't have these abnormal ones during the same day.
As usual, ask any questions you'd like.