Fifteen years ago, in Lafayette, Louisiana, a little boy named James Leininger started having nightmares. Whenever his mother came to comfort him, she would find his body contorted, his arms and legs scrambling for purchase, as if he were struggling to extricate himself from something. The two-year-old repeated the same phrases over and over: “Airplane crash! Plane on fire! Little man can’t get out!”

Over the next few months, the dreams became more detailed. James told his parents that he had been a pilot. He’d been shot down by the Japanese. He’d been the little man who couldn’t get…