Perhaps unrelated, but when I'm incredibly fatigued and on the verge of sleep, my memory seems to acquire an almost savant quality. For example, I can will arbitrary images to appear in my mind's eye, or effortlessly invoke the vocal tics and subtle inflections of people I've been close to, and generate muted mental conversations in their voice — something I'm never able to do during ordinary waking hours. It's like briefly unlocking a superpower. I wonder if the brain operates in a different way in those liminal spaces between sleep and waking.