Go South Meaning

(idiomatic) To become unfavorable; to decrease; to take a turn for the worse.

Example:   I should have walked away from the casino when my luck went south, but I stayed and ended up in the hole.
  He was unconcerned that his health might turn south.
  Yesterday the stock market moved south, ending up on a loss for the day.
  Afterward, when company profits had ventured a bit too far southward, the CFO began to get nervous.