[superk]

When this happens to me – the hour or so I'm awake in the middle of the night is not a peaceful relaxing time – the night has this pessimistic quality to it: the assignment I'm working on is impossible, I'll never get it done, I'll lose my job, that pain in my side is likely cancer, etc.. with that on my mind I drift back into a turbulent sleep after a while, but when I wake to daylight all those problems seem trivial and I'm able to get up and cope with the day. If anyone else experiences something similar that's probably why medicating a full night of sleep is so widespread...

[rhynie]

A while back I trained myself into the habit of sleeping in two cycles each night. I’m a night owl, and thought it would be a good way to get a full night’s sleep and still have the night owl lifestyle. After several months, I found myself feeling detached from the world.

The hour or two you get is literally between sleep cycles. During that nighttime, my mind would race and worry about the most useless things. The dreamlike state wouldn’t shut off cleanly and I could not concentrate, so that hour was never productive like I usually am during the night hours. It was impossible to learn anything, nothing would be retained. The second sleep cycle was always turbulent and I found myself waking up several times throughout. During the day, it felt like my emotions were muddled, like I was an automaton. That hour or two morphed into my only personal time, and the day became mindless, numb.

I considered this a failed experiment and re-trained myself back to a single sleep cycle. It was harder going back than it had been to split in the first place. After several months of ‘normal’ sleep I was back to having deep peaceful sleep. I was myself again during the day. I could learn and keep knowledge. The world was interesting again and I was engaging with it.

These were my experiences and expect it would be different for each individual.