The EU accepts a gift from Athens
Since a multitude of spontaneous worries will drive you nuts, it helps to have a few already scheduled so you can give them your full attention.
For example, I've penciled in "Worry about the Greeks" as today's contender.
It was going to collapse and then the EU would crack. Grass would grow in the streets, wolves would chase away the remaining tourists, and no banker from Germany would ever be able to visit Athens again. The story consumed a lot of news space until it didn't.
So if you want a manageable worry, Greece is a good choice.
But if you want a serious one, try the U.S. National Debt.