More than two decades ago, Peter Brugger, as a PhD student in neuropsychology at the University Hospital Zurich in Switzerland, was developing a reputation as someone interested in scientific explanations of so-called paranormal experiences. A fellow neurologist, who had been treating a 21-year-old man for seizures, sent him to Brugger. The young man, who worked as a waiter and lived in the canton of Zurich, had very nearly killed himself one day, when he found himself face-to-face with his doppelganger.

The incident seemed to have been started when the young man had stopped taking some of his anticonvulsant medication. One morning, instead of going to work, he drank copious amounts of beer and stayed in bed. But it turned out to be a harrowing lie-in.

He felt dizzy, stood up, turned around, and saw himself still lying in bed. He was aware that the person in bed was him, and was not willing to get up and would thus make himself late for work. Furious at the prone self, the man shouted at it, shook it, and even jumped on it, all to no avail. To complicate things further, his awareness of being in a body would shift from one body to the other. When he inhabited the supine body in bed, he’d see his duplicate bending over and shaking him.

Soon, fear and confusion took hold: Who was he? Was he the man standing up or the man lying in bed? Unable to stand seeing his double any longer, he jumped out of the window.