The Question and Answer section for The Open Window is a great resource to ask questions, find answers, and discuss the novel.
Framton already has anxiety: he is prone to being nervous and Vera's story pushes him over the edge.
Framton already has anxiety and freyed nerves. Vera's "ghost" story stresses out Framton even more.
As we know Vera could make up stories at a short notice and had made up the story to fool Mr.Nuttel which led to the use of ""mental excitement and violent physical activity"" which was to be absent.