Apparently the new research shows that our ancestors didn't sleep 8 hours straight but rather had what is called "segmented sleep", which was divided into "first" and "second sleep" with a period in between used for prayer, meditation, writing poetry, making love with your spouse (doctors recommended it for a better chance of conception) and even visiting neighbours in some cases.
The researchers speculate that it was the way our bodies adjusted to the long hours of darkness, especially during those winter nights, when it's dark for about 14 hours. It all started changing when the big cities such as Paris and Amsterdam introduced street lightning and segmented sleep virtually disappeared during and after Industrial Revolution with its cult of efficiency. It was considered wasteful just to spend so many hours in bed doing nothing and moreover, late evenings became a fashionable time for socialising.
The existence of segmented sleep explains something which has always puzzled me, namely the fact that monasteries used to have special midnight sermons (and some probably do now). It also shows that our ancestors probably used to lead a more relaxed lifestyle and enjoyed more rest than we do now.
The interesting thing is that some doctors speculate that the two-hour interval between the first and second sleep was important for stress reduction, as during this period of being not totally awake and not fully asleep the pituitary gland produced high levels of prolactin, a stress-reducing hormone.
If you are interested in this topic, here are some links:
The long and short of bimodal sleep
Your Ancestors Didn't Sleep Like You
The myth of eight-hour sleep
If you wake up in the middle of the night, it doesn't necessarily mean you suffer from insomnia. It can just be that your body tries to revert to the ancient sleeping patterns!