The above linked article talks about sleeping in shifts. People used to sleep when it got dark, and sleep for a few hours. Then they’d get up and do something. Pray, meditate, have sex, etc. Then, the second phase of sleep would begin and last until morning.
It was not until recently that people tried to sleep through the night. Plus, they were able to stay up later, because of modern lighting.
I have been thinking about this article and I wonder if what we currently call insomnia is just our bodies going into natural sleep patterns. Now, in the gap between first and second sleep, we have the option to do more things, because we can see what is going on. TV, reading, etc. Are we supposed to be waking fully and doing these things, naturally? The article was very interesting to me. It is worth reading.