Here's mine from Leave It to Psmith by P. G. Wodehouse (p. 20)
Exhilaration is a heady drug; but, like other drugs, it has the disadvantage that its stimulating effects seldom last for very long. For perhaps ten minutes after his uncle had left him, Freddie Threepwood lay back in his chair in a sort of ecstasy. He felt, strong, vigorous, alert. Then by degrees, like a chilling wind, doubt began to creep upon him--faintly at first, then more and more insistently, till by the end of a quarter of an hour he was in a state of pronounced self-mistrust.