Whether this has happened to you once or occurs every night like clockwork, many people experience the phenomenon of feeling tired during the day but getting a burst of energy right before bedtime.
Dr. Teofilo Lee-Chiong, MD, a sleep expert and professor at National Jewish Health, told us that "this phenomenon … which refers to a temporary increase in energy in a person who is fatigued or sleepy … is sometimes referred to as 'second wind,' and has many possible causes in different individuals."
INSIDER spoke to several doctors and sleep experts on the many culprits that contribute to this sleep-related phenomenon.
Terry Cralle, RN, clinical sleep educator and Saatva sleep consultant, explained that "adults have two peaks of alertness during the day, one in the morning and again in early evening. We often call that second peak the forbidden zone or wake maintenance zone (WMZ)."
Humans have a circadian alerting system — an internal biological clock that regulates the timing of periods of sleepiness and wakefulness throughout the day — as well as a homeostatic sleep drive, which is the body's natural drive to go to sleep as the day grows long. However, during this second peak of wakefulness (about two to three hours before bedtime), the circadian alerting system counteracts the bodies natural urge to sleep and forces us to wake back up.
"Some researchers theorize that humans evolved this way so that they could be alert to the dangers posed by predators that came out at night," Cralle said.
Dr. Lee-Chiong explained that if someone feels fatigued during the day, they will rest or take a nap to treat the sleepiness, which "results in the increased energy at night."
Dr. Sanam Hafeez, neuropsychologist and faculty member at Columbia University, says that "common practice daytime naps are not an adequate way to complement your nightly sleep deficit … daytime sleeping can exacerbate your insomnia and have a negative effect on your homeostatic sleep drive."
The monotony of your job could be contributing to your low daytime energy levels.
"Boredom and monotony can depress energy levels at any time," Dr. Lee-Chiong explained. Dr. Hafeez added that "People that lead sedentary lifestyles tend to report a greater amount of dissatisfaction with the quality of their sleep at night. This is because the body itself has not undergone exhaustive energetic output. If you have a monotonous job your brain might also come awake once it leaves work. This causes you alertness later at night."
For the majority of people with desk jobs, Dr. Hafeez says it's important to "take walks, do cardio, or try high-intensity interval training to get your body spending some of that energy." However, Joyce K. Lee-Iannotti, MD, the director at the Sleep Disorders Center at Banner University Medical Center in Phoenix, points out that exercise done within three hours of bedtime will actually arouse the body and potentially increase insomnia.
Most people tend to wind down at the end of the day by scrolling through their phone or watching shows on their laptops or tablets. However, phones and other screens emit blue wavelengths that boost attention and reaction times, which is not a desired response before bedtime.
"Melatonin is produced in your brain to help you sleep, but when you stimulate your eyes with blue wavelength before bed, it actually suppresses your melatonin production," Dr. Lee-Iannotti explained.
The more often you scroll through your phone before bedtime, the more it becomes learned behavior and your body comes to expect it and prepares to be stimulated. This is called conditioned or learned arousal, and it means that "you did something in your sleep environment [like habitually staring at your phone every night] that tells your brain that you should be awake or you should be aroused instead of being tired and ready for sleep … If it happens on a consistent basis, then you start feeling tired during the day because you're not getting enough sleep."
To combat this, Dr. Lee-Iannotti says it's important to practice good "sleep hygiene," which means your bedroom should be used for two activities, sleep and sex, and nothing else. That means no phones, no tvs, no media.
Dr. Lee-Iannotti says that psychophysiological insomnia is when a person's mind races at night and keeps them awake before bed. She explains that bedtime could potentially be the first time all day that you're not busy, making it an ideal time for stressors and anxious thoughts to flood your brain, keeping you awake.
Dr. Meir Kryger, MD, an expert in sleep disorders at Yale Medicine, says that "being tired in the daytime and energetic at night is usually caused by circadian rhythm abnormalities," explaining that it means that "a person's body clock runs late and they have a burst of energy in the evening." He says that people often develop this condition in their mid to late teenage years, though it can also be genetic.
This particular circadian rhythm abnormality is called "delayed sleep phase," and Dr. Kryger says the best way to deal with it is to take advantage of it, i.e. find a job that suits that sleep lifestyle or get work done during that burst of energy.
Alex Spinoso, MD, MBA at Evolve Health, explains that our adrenal glands pump out cortisol and that our cortisol levels are "supposed to be the highest in the morning and then slowly go down by the end of the night." However, in individuals with adrenal dysfunction, or experiencing stress, cortisol levels do not taper off at night.
"When cortisol is high melatonin should be low, and when melatonin is high cortisol should be low," Carolyn Dean, MD, ND elaborates.
Melatonin is the hormone that regulates sleep-wake cycles, "So, if someone has higher stress-induced cortisol levels all day and it doesn't diminish in the evening, then melatonin is blocked and the body feels revved up with cortisol," according to Dr. Dean.
Dr. Spinoso says that irregular cortisol levels can be tested with a saliva or urine test and a dose of hydrocortisone can often solve this issue.
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