Why can’t I sleep at night but sleep fine during the day?

Q:  I’m having trouble sleeping at night, but have no problem napping during the day.  Why is this?  And what can I do to sleep better at night?

There are many possible overlapping reasons, including a conditioned negative response to sleeping at night, or you might have a circadian rhythm disorder.  The culprit could be an underlying medical condition, side effects from prescription drugs, or even something as simple as too much caffeine too late in the day.  A checkup with your doctor will help you determine the specifics.

What we can say with some certainty, however, is that in general our minds and bodies have evolved to sleep at night when it’s dark, and be active during the day when it’s light.  To do the opposite, while certainly possible and in fact done by many, tends to work against the way we are designed.

A number of mental and physical systems specifically support sleep at night and activity during the day.  The two most important of these are the circadian rhythm and the homeostatic sleep drive.  These are the two metabolic processes that largely control sleep.

Circadian rhythms are the 24-hour cycles of day and night.  Our biologic systems have evolved over the eons to work along with these daily cycles.  We normally have peaks of energy during the day, then lulls at night when we sleep.  During sleep our bodies are replenished with energy for the next cycle.  During sleep our minds process information from the previous day and are re-set emotionally for a new one.

These processes occur very regularly each day and night, and they in turn are controlled by our master biological clock, which regulates our natural rhythms.  The external cue the biological clock uses to synchronize to each day’s cycle is very simple:  light.

Our sleep drive is a separate metabolic function in addition to the circadian rhythm.  Sleep drive is the biologic pressure to sleep.  It builds up over the course of a day.  The longer one is awake, the stronger the drive is to sleep.  After about 16 hours of nonstop wakefulness, we generally feel a strong urge to sleep.

When these two processes are working together in alignment, the sleep drive powerfully reinforces the circadian rhythm, and sleep at night becomes easy and natural, in fact practically irresistible.  And the longer we go without sleep, the more irresistible it becomes.

So if you are awake at night but sleep fine during the day, one possible explanation is that your biological clock is off by roughly 12 hours.  If that’s the case, it’s possible to reset it by using light.

Light is the simple environmental cue that synchronizes our biological clocks to the natural 24-hour circadian rhythm.  Light also stimulates the brain to start tracking prior wakefulness for the sleep drive.  So just as travelers with jet lag adjust to new time zones over a period of several days, you too can incrementally change the timing of your biological clock, a process known as entrainment.

To effectively use light for this purpose, it’s important to sleep in a dark bedroom, and upon awakening immediately expose yourself to bright light.  Broad spectrum natural sunlight is best for this purpose.  To help induce sleep, for an hour or two before bed try to limit your exposure to bright light.

Your sleep system also works better with consistency.  So once you’ve entrained your biological clock to your new sleep-wake schedule, it’s also important to have some regularity, especially with your wake-up time.

You can also use exercise to help strengthen your internal biological clock.  Some evidence suggests early afternoon is the best time to do this.

If you are the self-help type, you’ll find much more information about improving sleep in cognitive behavioral therapy for insomnia (CBT).   CBT is a collection of common sense methods to help you establish regularity and control over your circadian rhythm and sleep drive right away.  It will also help you counter any possible conditioned negative responses you may have developed about your bedroom and sleeping at night.

For more, see the “Sleep Principles” section of the Sleep Training System.

Explore posts in the same categories: Health, Insomnia, sleep

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3 Comments on “Why can’t I sleep at night but sleep fine during the day?”


  1. […] possible factor has to do with the alignment of your homeostatic sleep drive and your circadian rhythm, two key physiologic components that control […]


  2. […] of the most important controllers of sleep — circadian rhythm and sleep drive — are keyed to one unbroken period for sleep at night when it’s dark, […]


  3. […] re-establishing a normal circadian rhythm is very similar to what travelers do when recovering from jet lag.  Generally, most people take about a day to adjust to each hour of time difference.  So if you […]


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