This obsession with eight hours of continuous sleep is largely a creation of the electrified age. Back when night fell for, on average, half of each 24 hours, people slept in phases. In “At Day’s Close,” a remarkable history of night in the early modern West, Roger Ekirch writes that people fell asleep not long after dark for the “first sleep.” Then they awoke, somnolent but not asleep, often around midnight, when for a few hours they talked, read, prayed, had sex, brewed beer or burgled. Then they went back to sleep for a shorter period. Mr. Ekirch concludes, “There is every reason to believe that segmented sleep, such as many wild animals exhibit, had long been the natural pattern of our slumber before the modern age, with a provenance as old as humankind.”

In an era when we are trying to cram as much into a day as we can, Americans think about sleep as a biological function that needs to be managed. Mr. Hollan’s patients, he writes, think about sleep as a problem that interferes with more important things.

What have we lost with our dismissal of what the writer George Sturt called the “quiet depths of darkness”? In traditional non-Western societies like the Toraja, what happens at night really matters. People pay close attention to their dreams, and because they are awakened more often, they have more opportunity to remember them. When the anthropologist Eduardo Kohn arrived in a small village deep in the Amazon, people slept largely outdoors in an open thatch house, surrounded by other people. They would wake at night to drink tea, because it was cold, or because of the calls of animals. “Thanks to these continuous disruptions,” he writes, “dreams spill into wakefulness and wakefulness into dreams in a way that entangles them both.”

To my mind, the intriguing question is whether different sleep cultures encourage different patterns of spiritual and supernatural experience. That half-aware, drowsy state is a time when dreams commingle with awareness. People are more likely to have experiences of the impossible then. They hear their mother, many miles distant, speaking their name, or they see angels standing by the window, and then they look again and they are gone.

As an anthropologist, I set out to understand the way people experience the spirit. I’ve talked to many American evangelical Christians about the way they have experienced God. Recently, I spent time in similar evangelical churches in Accra, Ghana, and Chennai, India. One of the more startling differences is that Christians in Accra and Chennai say that God talks to them when they sleep, and in their dreams. He wakes them up by calling their names. American subjects, asked about odd events in the night, were more likely to say things like this: “I see things, but it’s just sleep deprivation.” It seems likely that the way our culture invites us to pay attention to that delicate space in which one trembles on the edge of sleep changes what we remember of it.