The worst kind of worries are the one that’s not necessary.
You woke up one day, you know you will have an exam at that day, and you cannot be at ease the whole morning. Or, you know you had a bad performance, and tomorrow you will have a review with your boss. You’re worried you may get fired. Another kind, you know that had screwed up, and now you have to be responsible with it.
It’s good to be worried. That’ll make you awake and aware. But, if you just get through it, do your best, you know you will feel better and think that your worries are unnecessary.