This:
""Second sleep" refers to a pre-industrial, biphasic sleep pattern where people woke for an hour or two after an initial 3–4 hour "first sleep," then returned to bed for a "second sleep" until dawn. Popularized by A. Roger Ekirch, this historical, segmented routine was common in Western civilization until the 19th-century rise of artificial light and industrialized schedules.Key Aspects of the Second Sleep Pattern:The "Watch" Interval: The middle-of-the-night waking period, often called "the watch," was used for activities like reading, praying, reflecting, visiting neighbors, or working.Natural Rhythm: Studies suggest this pattern is a natural response to long, dark nights, and some people naturally revert to this, which explains 3 a.m. awakenings.Disappearance: With the advent of artificial lighting and factory schedules, this split sleep pattern was largely replaced by a single, continuous 8-hour block by the early 20th century.Significance: It was once common in Western Europe, Africa, and Asia, and it is still seen in some studies where people live without electricity.The modern "3 a.m. wake-up" often causes anxiety, but many historians and sleep experts consider it a biological hangover from this once-universal habit."