Until I was five I shared a bed with my sister, 3½ years older than me. After our parents had switched out the light we would chatter away in the darkness until we fell asleep. But I could never afterwards remember falling asleep. It was always the same: one moment I was talking to my sister in the dark, and the next I was waking up in a sunlit room having been asleep all night. Yet every night there must have come a time when I stopped talking and settled down to sleep. It was incomprehensible to me that I did not experience that, and never remembered it.