Ordinary sleep advice assumes you control your bedtime. Millions of people do not. These guides look at the extreme version of that problem — a steel hull with no daylight, an ocean crossed alone, a winter with no sunrise, a job that wakes you with an alarm and gives you eighty seconds — and pull out what actually held up under measurement.
The series
- How do submariners sleep? — hot racking, and the 18-hour day the US submarine force ran for decades before abandoning it in 2016. On a 67-day patrol, cortisol adapted to the schedule and melatonin simply refused to.
- How do solo sailors sleep? — why the nap is capped at about thirty minutes (a ship below the horizon arrives in that time), what a study of 99 ocean racers found, and why polyphasic sleep is a survival tactic rather than a life hack.
- How do people sleep in Antarctica? — the polar night costs about 65 minutes a night, but constant summer daylight is no kinder. The problem is flat light, and the fix is contrast.
- How do firefighters sleep on shift? — eighty seconds from deep sleep to the truck, against sleep inertia that lasts fifteen to thirty minutes. Plus the finding that 37% screen positive for a sleep disorder and most do not know.
- Did people really sleep in two shifts before electricity? — the historical case for “first sleep” and “second sleep”, the 1992 experiment that seemed to prove it, the 2023 paper that challenges it, and what happened when three societies without electric light were actually measured.
What they all agree on
- Anchor to 24 hours, whatever hours those are. A consistently awkward schedule beats a drifting reasonable one. This is the single clearest finding across all four.
- Light is a timing instrument, not a sedative. Bright early, dim before your low point. It shifts when you sleep; it does not make sleep deeper.
- Planned split sleep is real sleep. What harms people is unplanned fragmentation, not a deliberate second bout.
- Your clock moves about an hour and a half a day at best. Even with optimised light. Flipping your schedule every weekend asks for something biology cannot supply.
- Preparation rituals are worth less than in-the-moment tactics. Among Mini Transat skippers, neither having a pre-race sleep strategy nor which one they chose changed their finishing times.
If your own hours are set by a rota
The shift-work guide covers the practical protocols for nights, rotations and early starts. A week with the sleep diary separates a timing problem from a depth problem, which need completely different fixes.
The shift worker’s guide → · Free sleep diary → · Resetting your body clock →
More of these are planned. If you work somewhere that makes sleep difficult and you think it deserves the same treatment, tell us.