Worry is repetitive thinking about past or future events. Hence, worry is the opposite of the here and now.
Depite all the negative press surrounding worry, it has an adaptive function to work through and solve problems. It’s like trying to solve a Rubik’s Cube- the more you twist and turn and look at it from different angles- as long as you persevere, you will eventually solve it.
So worry makes our concerns transportable, so that you can think about your problems at any time, which can be an advantage or disadvantage. But this depends if you are using your brain, rather than being run by it. But it is easy for this worrying to become a habit, and it can take on a life of its own- in this way, you are being run by your brain. But it does not have to be this way- you can find ways to use your brain, and therefore it can help you to solve problems.
On the upside, most things you worry about never happen. Worry also has an adaptive function in that it distracts you from more disturbing problems and emotions that you are not able to process right now.
On the downside, too much worry and too little worry leads to decreased problem solving and effectiveness (inverted-U). So for optimal problem solving and effectiveness, you need moderate amounts of worry.
With regards to origin, worry is from the thinking part of the brain, the cortex. Hence, worry is a cortical function.