Rukayya has not had a panic attack in her life. What she has is a running commentary.

She lies down at eleven and the commentary starts. The email she sent on Thursday and how it might have read. Her mother's blood test. Whether the front door is locked. Whether she is the sort of person who forgets to lock doors.

None of it produces a surge. It just does not stop. By one in the morning she is still awake, and by then she is worrying about not sleeping, which is a new item on the list.

That is worry. It is not weakness and it is not a character flaw. It is a habit of thinking that has got very good at itself.