2630 Mammalian Comfort.

It’s funny because being on meds for just over a year, I’ve noticed that I had been sleeping like that more and more, and then sure enough just as we were hitting winter this year, I went from doing two sessions of sleep every few days to it being a daily occurrence. I’ve definitely attributed the shift due to the little amount of daylight I’ve been getting up here in northern latitude land

Not only that but it also has a neurological impact on sleep, the second sleep thing is actually almost impossible when you have artificial light around. Studies were done to try and replicate the phenomenon and simply going to bed early and not needing to be up until late wasn’t sufficient by itself, people either took forever to fall asleep or woke up early and couldn’t get back to sleep, either way they did their normal sleep cycle of one block, however long that block is for those people. It wasn’t until they had some subjects go to only using natural light sources like the sun and candles and not being around electric or chemical lights at all for a few weeks that they started to naturally fall into the two sleeps schedule, even when they weren’t trying to deliberately invoke it, like for instance if they stayed up until late so they could do all the sleep in one block until dawn or later, they still woke up in the middle of the sleep cycle for a couple hours and then felt a strong need to return to bed for another cycle.

For reference a full REM cycle lasts roughly four hours, IIRC it takes around 3.5 hours to go through stage 1-4 of sleep and around a half hour to go through REM, after completing REM the body is really close to awakening, but if it doesn’t then it goes back to sage 3 and cycles between stages 3, 4, and REM a few times before awakening. Overall, for most people, this process lasts around 8 hours, under the two sleep model, however, you wake up after the first REM and then when you return to bed in a couple hours you start over again from stage 1 and awaken again after REM finishes again. This is why the body needs at least 4 hours of sleep to be properly functional, because you need to hit REM at least once and complete it. If you pull an all nighter before something important like an exam or work or whatever and you have a few hours to spare before you need to get going, if you have less than 4 hours you are better off staying up the whole way through than catching 1-3 hours of sleep, because interrupting the process part-way leaves you groggy, disoriented, and with rather poor cognition for a good, long while.