Epicurus told us that anxiety is worse than bodily pain. Present suffering soon passes; anxiety lasts a long time and undermines an otherwise happy life. He was right, and pharmaceuticals are not the answer; they only mask the problem. Many of them become less effective with time and I can think of one positively dangerous drug that makes things a lot worse.
I rather subscribe to the view that persistent background anxiety is actually chemical in nature, maybe an inherent trait in individuals and may be reduced a bit by meditation or reading a book, but seldom eliminated. Outside events and circumstances might trigger particular attacks, but there are some people into whom anxiety is hard-wired. It is possible that this is an ancient survival mechanism, a way the human being deals with perceived or possible threats in a hunter-gatherer society where there is no law and no rules.
I like the idea of the bell curve in things like this: the mass of people occupy most of the curve, well-balanced and modestly anxious over specific matters. Then, at the extreme ends of the curve there are those who are either in a constantly elevated state of nerves or who are never anxious at all. Some think the latter have no imagination!
Come to think of it little has probably changed in ten thousand years.