“The book’s most interesting chapter is called “The Watch”. It’s about that hour or two of wakefulness which occurs in the middle of the night, between the first sleep and the second sleep. You know the one…right? Neither did I, but apparently, this makes us a bit weird, historically speaking.
Warren says that until the era of artificial lighting and alarm clocks, sleep was segmented. It was common for people to sleep twice each night, with a bout of awakeness in the middle. This nocturnal alertness wasn’t quite like daytime waking, though: it was more relaxed, less focussed, carefree.
There are two lines of evidence for this. Writings from the pre-modern era routinely make reference to “first sleep” and “second sleep”, and in many languages, although not modern English, there were special words for these periods and the wakefulness between.”