Besides if I were a devout Calvinist (and I somehow can't remember Calvin's name coming up anywhere in the Bible ... but let that pass) then I would worry or not worry based on what God had pre-ordained from all time.
So to answer your question (from a Calvinist perspective): some people will worry and some people won't worry just cuz God determined that they would or would not worry. And because God is perfect and His creation is perfect people will only worry or will only not worry at those precise instances in time when God's perfection demands it.
Obviously being puny unimportant avatars we are completely incapable of understanding why it is that some people worry and some don't and that some people worry sometimes, but don't worry other times. We don't have a clue as to how this fits into God's perfect plan for all of humanity.
But from a non-Calvinist point of view people can freely choose to worry or not as they please. And having free independent beings in a universe all of a sudden makes it a much more interesting place that is more worthy of an almighty God, and not just a mere computer gamer.
Is the natural man "free" to choose righteousness?
And having free independent beings in a universe all of a sudden makes it a much more interesting place that is more worthy of an almighty God
Worthy? You believe fallen man is "worthy" of God?
Read Romans.