Anxiety is normal and only considered a disorder when it significantly interferes with day-to-day living. A critical element of treating most anxiety disorders is exposure. Basically, exposure involves facing what you fear. Depending on your specific fear, this exposure can either be real or in the imagination. For example, someone with a deep fear of cats might start out by thinking about cats, talking about cats, and looking at pictures of cats. Then after those situations become routine, that person might go to a shelter and look at cats, then progress to touching cats.
Treating some fears, like fears of getting cancer, obviously can’t be combated by real exposure. You wouldn’t suggest that someone expose themselves to cancer-causing chemicals to beat a fear of getting cancer. A common way of getting around the issue would be to imagine or talk about “the worst case scenario.” That technique involves exposure in the imagination. So, someone with overwhelming fear about getting sick might be asked to describe the most feared outcome. Exposure might involve several sessions of describing, imagining, and thinking about that worst case.