This kind of tiredness keeps its own hours. In the morning you can still push through. By two or three in the afternoon your eyelids feel heavy, and you have to read a paragraph twice before it sinks in. Yet by ten at night, just when you ought to feel sleepy, your mind clears. Some people also wake in the middle of the night at about the same hour, night after night. In many people, the body’s day–night clock runs out of step with the schedule they have to live by. It is as if they carry a different time zone inside them.
Light sets the time on the body clock
That clock needs resetting every day, and the strongest signal for setting it is light.
Wright’s group (2013) measured the body clock of a group of people during their normal lives and again while camping, with only natural light. Living indoors, people get little daylight during the day and a lot of electric light after dark, so the internal clock gets pushed later. Outdoors, the clock lined up with the sun again: the biological night, meaning the stretch of time the body treats as night, ended right after sunrise, even before waking time. Night owls shifted earlier the most, ending up close to people who are naturally early risers.
Once the clock has been pushed later, the alarm can go off while the body is still in its biological night. You manage to get up, but stay foggy all day. In the evening, by the internal clock, it is still early.
Evening screens push bedtime later
Many people lie in bed scrolling on their phone, waiting to feel sleepy before they put it down. The experiment by Chang and colleagues (2015) comes close to that habit: participants read for a few hours before sleep, sometimes on a light-emitting e-reader, sometimes from a printed book. On the evenings they read on a screen, they took longer to fall asleep, felt less sleepy, released less melatonin (the hormone that tells the body it is dark), and their body clock shifted later.
The next morning they were less alert. When looking for the reason behind daytime tiredness, the doctor also asks about the evening before.
Late meals also pull part of the body clock out of line
People who get home late from work often eat dinner when it is fully dark, some days close to bedtime. Besides the central clock in the brain, many tissues in the body have their own clocks, and these also listen to mealtimes. When Wehrens and colleagues (2017) had 10 healthy young men shift their three meals 5 hours later for 6 days, the melatonin and cortisol rhythms of the central clock did not change. Only the blood sugar rhythm shifted later, by about 5.7 hours. When you eat late, the brain and the organs may run on two different times. This was a small study done only in young men, so it should be read with caution.
Workdays and days off on two different rhythms
Preferred sleep timing, also called chronotype, varies quite a lot from person to person and is largely set by the body clock (Wittmann et al., 2006). School and work schedules are the same for everyone, so night owls run short on sleep all week and then catch up on days off. The authors call this gap social jetlag. In people under 25, chronotype was clearly linked with how mentally well they felt and with their use of stimulants, and the authors believe this is largely due to that gap.
Waking in the night, as traditional medicine sees it
Traditional medicine divides the night into five watches, and the full day and night into twelve two-hour periods named after the animals of the zodiac. Meridian theory links each of these periods with one meridian that is at its peak, often called the meridian clock. The Chou hour (丑时 / 丑時, chǒu shí), from 1 to 3 in the morning, around the fourth watch, corresponds to the Liver meridian (Zu Jueyin Gan jing).
If you keep waking at around 1 to 3 a.m. for many nights in a row, a traditional medicine doctor will look closely at the Liver: asking more about pent-up frustration, alcohol and beer, and rich, oily dinners, then comparing this with your pulse and tongue. That is a lead for the examination, not enough for a conclusion; some people wake at that hour simply because they need to urinate at night or the room is too hot.
Waking in the night and struggling to fall back asleep is also linked with a prolonged state of alarm in the nervous system; this is covered in our article on insomnia.
How we examine afternoon tiredness and night waking at Tam Duc
The consultation starts from specific times: what time you get up on workdays and on days off, when you eat dinner, when the screens go off, and what time you wake in the night.
The doctor does a clinical examination and the four examinations (looking, listening, asking, taking the pulse) to identify the pattern, and muscle testing in Applied Kinesiology (AK) to see how far stress is contributing; stress is covered in our article how stress affects your health. Long-lasting tiredness can also come from anemia or thyroid disease, so when either is suspected, the doctor orders blood tests first.
For people who often wake between 1 and 3 a.m., the doctor teaches one more thing to do right there in bed: lightly tap your fingertips around your temples (temporal tapping) while silently repeating a short affirmation, such as “My body is safe to sleep deeply.” The aim is to give the body a familiar routine each time you wake, instead of lying there watching the clock. The doctor shows you in person, during the examination, which way of tapping and which affirmation suit you.
Depending on the pattern, the doctor may combine acupuncture and an herbal decoction modified for each person, along with rearranging your daily routine to fit your real work schedule.
What kind of daytime tiredness and sleepiness needs an early check-up
A body clock out of step cannot explain every bout of tiredness. See a doctor soon if:
- The person who sleeps next to you hears you snore very loudly, with pauses of silence followed by a sharp gasp;
- You are so sleepy during the day that you nearly nod off while driving a car or riding a motorbike;
- Your tiredness comes with unexplained weight loss, a fever that won’t go away, or shortness of breath during light activity;
- You have felt low and lost interest in doing anything for several weeks.
The first two signs call for a check for sleep apnea; the last one needs an assessment by a psychiatrist. If you have ever had thoughts of harming yourself, tell someone close to you right away and see a psychiatrist that same day.
Worth keeping
- When you get up, go outside or stand by a bright window for a while before turning on the computer;
- For a few hours before sleep, read a paper book instead of your phone or tablet;
- Move dinner earlier and keep mealtimes about the same from day to day;
- Keep the gap between your wake-up time on days off and on workdays as small as you can;
- If you wake between 1 and 3 a.m., lie still, tap your temples lightly and silently repeat your affirmation; don’t reach for your phone.
With people who feel drained in the afternoon, Dr. Dinh Ngoc Duc (MD, MSc in Traditional Medicine) often asks in detail about their wake-up time on days off. Many people sleep in until nearly noon without realizing that the gap has anything to do with their tiredness in the middle of the week.
References
- Wittmann M, Dinich J, Merrow M, Roenneberg T (2006). Social jetlag: misalignment of biological and social time. Chronobiol Int 23(1-2):497-509. https://doi.org/10.1080/07420520500545979
- Wright KP, McHill AW, Birks BR, Griffin BR, Rusterholz T, Chinoy ED (2013). Entrainment of the human circadian clock to the natural light-dark cycle. Curr Biol 23(16):1554-8. https://doi.org/10.1016/j.cub.2013.06.039
- Chang AM, Aeschbach D, Duffy JF, Czeisler CA (2015). Evening use of light-emitting eReaders negatively affects sleep, circadian timing, and next-morning alertness. Proc Natl Acad Sci U S A 112(4):1232-7. https://doi.org/10.1073/pnas.1418490112
- Wehrens SMT, Christou S, Isherwood C, Middleton B, Gibbs MA, Archer SN et al. (2017). Meal Timing Regulates the Human Circadian System. Curr Biol 27(12):1768-1775.e3. https://doi.org/10.1016/j.cub.2017.04.059
