To suffer inexplicable pain of some sort. This pain isn't necessarily physical, however. The usage of the word "world" doesn't always implicate a great length of time that the pain will exist, but rather the magnitude of the pain.
I spent my first year of college drinking and failing classes. Now Daddy won't pay my tuition, and I have to go to community college. I'm in a world of hurt!
Dad: Son, did you go outside without my permission again?
Son: (lying) No, Mom said--
Dad: *removes belt* You're about to be in a world of hurt!
Son: *starts crying even though he hasn't been hit yet*
Dad: Why are you crying? I haven't even hit you yet! But don't worry, i'm about to give you something to cry about.
...Not that that actually happened or anything...