The term “second sleep” refers to the concept of “segmented sleep” or “biphasic sleep,” which was common before the Industrial Revolution. In segmented sleep patterns, people would sleep in two distinct phases separated by a period of wakefulness in the middle of the night. During this wakeful period, individuals might engage in various activities such as reading, praying, or socializing before returning to sleep for a second phase.
This sleep pattern is often mentioned in historical records, literature, and medical texts predating the widespread use of artificial lighting. It’s believed that before the advent of electricity, people’s sleep patterns were more aligned with natural light cycles, allowing for a first sleep period after sunset, a waking period in the middle of the night, and then a second sleep period before sunrise.
With the introduction of artificial lighting and changing societal norms, such as the standardization of the 8-hour continuous sleep schedule, segmented sleep patterns gradually became less common. However, some people still experience biphasic sleep naturally or choose to adopt it intentionally as part of their lifestyle.