Bedtime Procrastination Even Though We're Tired

Two different things are usually happening when we feel tired, and they often diverge at night. One is how sleepy we feel, and the other is how quickly we'd actually fall asleep if we crawled into bed and actually tried. For most of the day, those two systems track each other closely enough that we never notice they're separate. Near bedtime though, they can split, and that split can be a main driver behind what keeps us on the couch insanely tired yet still awake hours past when we planned to go to sleep.

What Builds Up While We're Awake

While we're awake, our brain burns fuel, and one byproduct of that is adenosine. Adenosine is largely responsible for telling us when to get some rest, so the longer we've been awake, the more of it builds up and the harder it is to remain alert. Sleep clears it out. 

This is actually the pathway caffeine works on. It fits the same receptors adenosine binds to and blocks the “I’m tired” message, so the adenosine keeps climbing. We only feel the crash when the coffee or energy drink wears off and we finally notice how much of the tiredness signal was actually being blocked. The buildup we experience is often called sleep pressure, and we have to actually fall asleep to clear it out.

The Clock Pushes Toward Bedtime Procrastination

If sleep pressure were the only thing affecting us, we'd get steadily sleepier from breakfast onward and start losing the fight by mid-afternoon. We usually get more tired as the day goes on, but our body doesn’t usually force us to sleep because a second system pushes the other way. The other process keeps roughly 24-hour time and sends out a signal to stay awake that strengthens as the day goes on. It rises at roughly the same rate the sleep pressure does, which is what holds us awake through the whole day instead of making us break it into a multiple-naps-per-day kind of life.

That wake signal doesn't taper off as bedtime approaches though. It reaches its strongest point in roughly the last two or three hours before we normally go to bed. The hardest window of the whole day to fall asleep in was actually found to be the one immediately before our regular bedtime, so it’s called both the wake maintenance zone and the forbidden zone for sleep.

Shortly after that window right before bed, the pineal gland starts releasing melatonin, which is our body's internal announcement that it's dark out. Melatonin doesn't appear to sedate us so much as reduce the impact of the wake-generating system, and sleep onset follows closely behind the start of melatonin release. Light, whether natural or artificial, delays that release. That's a core reason bright rooms and screens late in the evening matter because it postpones the signal that ends the forbidden zone.

Why the Window is Later for Some of Us

Where that window falls can vary quite a bit person to person. Chronotype is the timing our internal clock is set to, and it’s mainly responsible for how late in the day our wake signal peaks and how late melatonin starts signaling us. Someone whose gate opens around half past midnight but who sets an 11 p.m. bedtime lands right inside their forbidden zone. Lying down at 11 likely means tossing and turning for a while before they actually fall asleep.

In a study observing how people felt when they went to bed, late chronotypes reported the most bedtime delay on Monday and Tuesday, but it faded as the week went on. This makes sense because by midweek, enough sleep debt has built up for the sleep pressure to overwhelm the evening wake signal. Getting to bed earlier stops taking so much effort because our physiology shifted, not because we found more discipline by Thursday. Exhaustion can be a helpful sleep drug.

The same study tested the obvious alternative too. Participants also rated how much self-control they felt they had left each evening, and within the same person, the nights with more perceived control were the nights with more bedtime procrastination, not less. On the nights they felt most depleted, they went to bed close to when they'd planned. 

Most Nights It Doesn't Feel Like a Decision

Asked to describe what actually happens, people who regularly go to bed later than they meant to usually don’t describe it as a choice. The most common explanation is losing track of time, so the intended bedtime passes without us even noticing it. Another reason is claiming an extra hour because the rest of the day belonged to other people. A third reason is just going to bed late because lying down earlier means lying awake. In those interviews, the three drivers often turned up in the same evening, one giving way to another as the night went on.

Underneath all three is the same structural problem. Going to bed is a stopping task, not a starting one. Nothing outside us really ends the evening, so the transition has to be launched internally at the hour when our body is doing the least to help us out.

Where the Extra Hour Goes

The delay in going to bed is lost time. The time we wake us is usually pinned by alarms and obligations, so an hour taken at the end of the day is subtracted rather than shifted. Logically, when we go to bed later and don’t compensate by sleeping in, it shows up the next day in sleepiness and in volatile emotions.

Knowing how all this works doesn't make going to bed any easier, but it helps justify that the effort is worth spending. Willing ourselves to feel sleepy at 9 is working against the wake signal at its strongest can be brutal, but when we know the cost, it can help us take the steps to shift our window so we go to sleep when we most need it.

References

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6. Kühnel, J., Syrek, C. J., & Dreher, A. (2018). Why don't you go to bed on time? A daily diary study on the relationships between chronotype, self-control resources and the phenomenon of bedtime procrastination. Frontiers in Psychology, 9, 77. https://doi.org/10.3389/fpsyg.2018.00077

7. Nauts, S., Kamphorst, B. A., Stut, W., De Ridder, D. T. D., & Anderson, J. H. (2019). The explanations people give for going to bed late: a qualitative study of the varieties of bedtime procrastination. Behavioral Sleep Medicine, 17(6), 753-762. https://doi.org/10.1080/15402002.2018.1491850