Here's a link to an interesting article on insomnia.
"In the early 1990s, psychiatrist Thomas Wehr conducted an experiment in which a group of people were plunged into darkness for 14 hours every day for a month. It took some time for their sleep to regulate but by the fourth week the subjects had settled into a very distinct sleeping pattern. They slept first for four hours, then woke for one or two hours before falling into a second four-hour sleep."
This describes exactly how I sleep!
The article goes on to explain that this way of sleeping (a first and second sleep) was the normal back in the old days. And how the modern thinking about people needing 8 hours sleep in a row is crap.
I've been off Ambien since August, and I'm still trying to figure out how to sleep. I've stopped trying to sleep for 8 hours. 5 or 6 is fine. If I wake up after 4am, I just stay up.
And now I'm using my weird sleep patterns to go swimming. I hit the pool as early as possible, then take my time in the sauna and getting ready for work.
I like thinking that I can find new & better ways to sleep, and that the pressure to sleep 8 hours in a row isn't the only way to sleep.
I'm going to sleep like the people did in the old days!