I recently listened to an interview with Matthew Walker (author of "Why We Sleep" book mentioned in article). Dr. Walker stated the scientific consensus is now trending toward historical biphasic sleep being a social trend rather than how we're "supposed" to sleep.

Matthew Walker's excerpt on biphasic sleep: https://delanceyplace.com/view-archives.php?p=3524 TL;DR: There's evidence of cultures untouched by electricity sleeping 7 hours at night with a 30-60min afternoon nap, which he calls biphasic sleep, with some tribes switching to monophasic in cooler months. All humans have a hardwired dip in midafternoon alertness.

> All humans have a hardwired dip in midafternoon alertness.

In my personal experience, if you don't have a post-lunch carbs crash and you do have air conditioning, the dip doesn't exist.

He doesn't really seem to back up the existence of a biological dip at all that is innate to human rhythms.

Isn't he claiming the opposite? (But I don't have the book to dig into the sources):

This brief descent from high-degree wakefulness to low-level alert­ness reflects an innate drive to be asleep and napping in the afternoon, and not working. It appears to be a normal part of the daily rhythm of life.

I've always understood it to be related to the hottest part of the day, not so much a post-lunch thing. Probably why GP mentioned air conditioning preventing it.

I believe the original parent is refering to the idea that people naturally wake up and do stuff in the middle of the night.

Yes, but I couldn't find where Matthew Walker says that.

True, I was referring to waking up in the middle of the night for an hour or two and then going back to sleep.

This was apparently limited to victoria england. Most hunter gather cultures slept one block at night and then napped in the afternoon, according to matthew walker.

My night time wakings have a very clear and strong association with those periods of time when I’m working on my side-project/startup. The bbc article mentions ‘meditating on your dreams’ as an activity for this time, however I’m likely to have a mind racing with all permutations of technical problems that I’ve evidently not managed to clear from my brain. Does anyone have experience-based advice on whether it’s better to try to do a few hours work at 3am vs. getting out of the bed and e.g. reading fiction (which I believe is the best advice to break the cycle of negative association that can build up if you are lying in bed awake and annoyed)

Personally I find that trying to work at 3am is a bad idea. The backlighting (no matter how much blue-light filtering you have) will wake you up, and even if you solve the problems that are keeping you awake now, you're almost guaranteed to get back in bed with new ones to be thinking about.

Fwiw, I put my screen in darkroom mode and use nothing red bulbs in my evening lights.

It's very easy to avoid bluelight while you work. However, as you mention, that's only half the battle.

My issue with this is that warm light encourages melatonin production so I end up dozing whenever I have red light or f.lux/Night Shift/etc on.

It doesn't.

I'd hazard you are sleep deprived.

Nobody ever made a good decision at 3:00 am. Keep away from the codebase please.

Insomnia probably isn't limited to a simple reflection of a biphasic sleep-related problem. As an example, someone with naturally high anxiety could get on the most biphasic sleep schedule possible and still suffer from insomnia due to their anxiety about what tomorrow brings, etc.

Sure. My point is not that insomnia doesn't exist, only that waking up in the middle of the night is not necessarily an indication of insomnia.

I sleep biphasically during most weekends. Partly because I work and work-out a lot during week days. By the time it's Saturday, I'm both mentally and physically exhaust. So, I need more resting and sleeping a few hours after lunch works well. In order not to make my sunday night hard to sleep, I sleep a bit less (6 to 7 hours) and then sleep a few more hours (~3 hours)

I heard about this through my interest in the French Middle Ages sociology.

I was always wondering, though how this worked in summer when the nights are short and one can hardly afford a meaningful break in the middle (if not napping in the afternoon)

What causes the deep relief of having made a full uninterrupted 7-9h sleep ?

I don't mind split nights but I'm still into the usual belief.