An old one but a good one!
One of the evolutionary advantages the human brain has is the ability to test out scenarios by imagining ourselves in different situations. This means we can safely try out strategies without actually putting ourselves at risk but feeling some of the emotion. Like most normal processes this can go wrong and one aspect of anxiety can be getting stuck going over and over a difficult situation rather than using it to plan a strategy to cope.
We've all done it: "what if I fail the exam", "what if I lose my job" and less commonly "what if I go for a job interview at the BBC as a data cleanser support worker and accidentally end up on TV being interviewed about an Apple legal case".
It's a Youtube classic, take it away Guy Goma, not Guy Kewney!
If you have ever wondered what anxiety looks like check out his face at the start of the interview, in fairness he also displays remarkable anxiety management!