History yields valuable insights regarding sleep. According to some recent research, until the age of electricity many people slept in two segments. They would wake up in the night for an hour or two, then return to sleep for another block of time. “The dominant pattern of sleep, arguably since time immemorial, was biphasic,” says Roger Ekirch, a sleep historian at Virginia Tech University and author of At Day’s Close: Night in Times Past. "Humans slept in two four-hour blocks, which were separated by a period of wakefulness in the middle of the night lasting an hour or more. During this time, some might stay in bed, pray, think about their dreams or talk with their spouses. Others might get up and do tasks or even visit neighbors before going back to sleep.”
References to “first sleep” or “deep sleep,” and “second sleep” or “morning sleep” abound in historical legal depositions, works of literature, and other pre-Industrial era archival documents. Gradually, during the 19th century, references to segmented sleep disappeared, Ekirch says,
"and now people call it insomnia.”
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