When does a day end? For most of us, the answer is pretty clear: sometime in the evening, at the latest when we go to sleep. We finish work, take care of a few more things, maybe tidy up the apartment (maybe!), watch another episode of a show, and eventually we go to sleep. That marks the end of the day. That sounds obvious, and somehow we automatically associate sleep with “recovering from the day”—from work, from stress, from the kids, and so on. The usual sequence:
Day → Activity → Night → Sleep
Ready for a change of perspective?
What if we viewed sleep as the beginning of the day—that is, as a “start to the day”? Sleep doesn’t just tidy up the previous day;it prepares us for the day ahead. The new sequence:
Night → Sleep → Day → Performance
At first glance, this sounds like just another way of putting it. In reality, however, it fundamentally changes the meaning of sleep, including in terms of mindset.
3 Shades of Day and Night
First, we need to define “day,” because there are three different ways of looking at what we mean by “end of the day” and “beginning of the day.”
- The concept of light (day) and darkness (night). The day ends with darkness and begins with light.
- The conventional view of the day. The day ends in the middle of the night at 24:00 and begins at 0:00, which … is a bit odd.
- The subjective day. Very few people are familiar with this concept. It is a term from the field of chronobiology. It begins with the body’s biological shift from regeneration to activity. Cortisol suppresses melatonin, etc.
This shows us that it is by no means clear whether the day begins with sleep or ends with it, given that the term “day” is not precisely defined. One more thing: If we view the term “day” as a 24-hour cycle, it also includes the night—that is, day and night at the same time.
Sleep as Preparation
In many activities, we take it for granted that preparation is part of the actual performance. An athlete warms up before competing. A pilot prepares himself and the plane before the flight begins. A musician tunes his instrument before the concert begins. No one would ever think to call this time “wasted.” Yet that’s exactly what happens when we push sleep to the end of the day—we see it as lost time that we associate with the day itself or with being awake. That’s why we lie in bed scrolling through our smartphones, watch one more episode of a show, and make another trip to the fridge—just so we don’t miss out on “life.”
But what happens when we turn our gaze in the other direction—not back to the day that has passed, but forward to the day ahead? Then sleep suddenly becomes a valuable period of preparation.
The subjective day is not our time
A brief note on the subjective day: The concept of a day as a clearly defined period from 0 to 24 hours is, in any case, a social convention. Chronobiology —or nature—takes a different perspective. It distinguishes between the external, social day and the subjective, or biological, day. The subjective day does not simply describe the time of day, but rather the phase organized by the circadian system as “day”—or, more accurately, as a period of activity. Accordingly, there is also a subjective night. These two phases do not necessarily correspond exactly to our clock. This becomes particularly clear with nocturnal animals. Their subjective day occurs during the phase of darkness—that is, at night.
This is particularly evident when it comes to chronotypes. What is already the dead of night for one person may still be part of another’s biological day—and vice versa. The biological day therefore does not begin and end simply because a clock displays a certain number; rather, it is defined by bodily processes based on regeneration or activity and is largely controlled by the SCN (suprachiasmatic nucleus).
The Curious Case of Midnight
This difference is particularly noticeable in people who go to bed late. Anyone who goes to bed at 12:30 a.m. has, according to our calendar time, already entered the new day. Incidentally, this is the case for over 70% of people… at least from a biological perspective, and over 80% during daylight saving time. Biologically speaking, one’s subjective night typically begins with the DLMO 2 to 2.5 hours before falling asleep. In this case, we begin the new calendar day shortly after the start of our biological night. Midnight is an administrative cutoff point. It is not a biological one.
It’s actually amazing: We’ve set a specific time for the new day to begin, even though a large portion of the population hasn’t even reached the start of their biological day at that point. For most people, the day begins mentally when they wake up, but not for their bodies.
And that makes a seemingly trivial question suddenly interesting: If there is a subjective day and a subjective night—which of these two phases actually comes first?
Which comes first, night or day?
What’s fascinating about this is that when we say in the evening, “The day is coming to an end”—strictly speaking, that means everything that comes next is already part of the new day. Before artificial light existed, no one had to artificially end a day. Light and darkness were not segments of a calendar, but fundamental conditions of life. And from this perspective, night doesn’t appear as what’s left over after the day. It is a distinct biological phase that prepares the body for the coming day. In the end, one question remains: Which came first—night or day? According to current research, in the history of the universe, darkness likely came first, which supports our simple model of thought.
A slight shift in thinking
My goal here is not to invoke science, but rather, through this more philosophical line of thought, to simply give sleep the place on the mental pedestal that it deserves. Perhaps that is precisely why we need a different perspective on it.
Furthermore, words also influence how we view things. “Sleep” describes a state, whereas “regeneration” already describes a function. Regeneration prepares us for something, builds us up, restores our energy, and focuses on the moment “x” when we open our eyes.
For me, sleep is DayPrep—not just cleaning up after a party. It’s not the day that hands the broom over to sleep; rather, sleep passes the baton to the day.
We don’t sleep to end the day. We sleep to prepare for the day.
Ready for a change of perspective?
