Sometimes, that afternoon slump can feel so strong, you promise yourself that you’ll get to sleep early. Heck, by 5 p.m., you might even fantasize about peeling back the covers and crawling into bed right then and there. But, come your intended bedtime that night, you get a burst of energy that precludes you from nodding off. On a spectrum of “lightly uncool” to “deeply annoying,” getting a second wind of energy near bedtime falls firmly on the annoying side.

According to sleep experts, there are several reasons why you might feel more alert than tired for a period in the evening close to your bedtime—even if you were just about ready to doze off earlier that day. Some of it has to do with your biology, but the behavioral choices you make throughout the day can also influence your pattern of alertness, triggering a second wind at night that prevents you from getting to sleep easily.

What is a second wind as it relates to sleep?

If you participate in or are a fan of endurance sports like long-distance running, you may know that a second wind refers to a burst of energy that arrives well after you tore through your initial stores of energy.

In much the same way, a second wind in terms of your sleep schedule typically refers to “an experience where someone starts to feel drowsy early in the evening but then gets a burst of energy after that initial sleepiness passes,” says sleep psychologist Jade Wu, PhD, sleep advisor for Mattress Firm. While anyone can experience a second wind, sleep experts say there are certain factors that make someone more likely to deal with a nighttime spike in energy.

3 reasons you might catch a second wind of energy right before your bedtime

1. Your circadian rhythm favors alertness in the evening

Much of why you might catch a second wind of alertness close to your bedtime could be tied to the unique characteristics of your circadian rhythm (the 24-hour internal clock that lets us know when we should be awake and asleep). It functions with the release of wakefulness-promoting cortisol throughout the day and sleepiness-promoting melatonin at night. But exactly how and when these hormones are released each day is determined in part by your natural biology—so, each person’s circadian rhythm has a slightly different pattern, or sleep chronotype.

“Everyone exists on a spectrum,” says Dr. Wu, “where most of us sleep between 10 a.m. and 6 p.m. or 11 p.m. and 7 a.m., but some people are biologically wired to feel most energetic and do their best work in the evenings.” These people have an evening sleep chronotype—meaning their brains don’t release sleep-promoting melatonin until later into the night—and are often referred to as “night owls.” If you fall into this camp, Dr. Wu says you may be more susceptible to a second wind at night because your circadian alerting system is still telling you to be awake when others may be winding down.

“Some people are biologically wired to feel most energetic and do their best work in the evenings.” —Jade Wu, PhD, sleep psychologist and sleep advisor for Mattress Firm

Certain behaviors can also influence your circadian rhythm, shifting back your brain’s release of melatonin and leading to a spike in alertness in the evening. Case in point: anything that involves stimulation, whether intellectually or visually. If you spend the hour or two before bed catching up on social media or watching movies or TV, the intellectual stimulation and blue-light exposure can interfere with your typical circadian alerting system.

“Your brain could get confused about what time it is, prompting an adrenaline response that causes you to stay alert for longer,” says sleep psychologist Janet K. Kennedy, PhD. (Yes, even if you’re actually in need of sleep.) That’s why she suggests creating a “buffer period,” like a calming bedtime routine, between those stimulating activities and your actual bedtime, in order to avoid confusing or delaying your natural circadian rhythm.

2. Your daytime behaviors reduce your homeostatic sleep drive

Concurrent to your circadian rhythm guiding when you generally wake up and when you get sleepy over the course of a 24-hour period, your homeostatic sleep drive—which is basically your appetite for sleep—also builds throughout the day, says sleep-medicine physician Vishesh K. Kapur, MD, MPH, founder of the University of Washington Medicine Sleep Center.

This process hinges on the development of a chemical called adenosine in the brain, which is influenced by your behaviors. For example, “physical movement, activities, and exercise cause the cells in your body to break down adenosine triphosphate (ATP) for fuel, which leaves you with more adenosine, increasing your sleep hunger or drive for sleep,” says pulmonologist and sleep medicine specialist Raj Dasgupta, MD. This is why you might normally feel increasingly tired as you go about your day and approach your bedtime.

But at the same time, there are also behaviors that can equally reduce your sleep drive, counteracting the above process and leaving you with a second wind at night. For instance, “caffeine is an antagonist of adenosine,” says Dr. Kapur, “so when you consume caffeine, you’re blocking the activity of the chemical that tells your brain it’s time to sleep.” While having a cup of coffee or caffeinated tea in the morning still allows your body plenty of time to build up adenosine (and get sleepy) throughout the rest of the day, if you go for an afternoon or evening caffeinated beverage, the adenosine-blocking affect could leave you more wired than tired come your bedtime. Even drinking large amounts earlier in the day can lead to you feeling more alert as bedtime nears.

“When you consume caffeine, you’re blocking the activity of the chemical that tells your brain it’s time to sleep.” —Vishesh K. Kapur, MD, MPH, sleep-medicine physician

Napping plays a similar role here because naps can chip away at the stores of adenosine your body has been accumulating all day, says Dr. Dasgupta. If you think of your sleep drive as “hunger” for sleep, then naps serve as little snacks; and just like snacking before a meal can shrink your appetite at that meal, napping before bedtime can minimize your sleep hunger, giving you that second wind of energy when you least want it.

That’s not to say you can’t nap at all—but just that you should pay attention to the length and timing of your naps. “If you’re just keeping the nap to 20 minutes, you will technically just be entering the light stages of sleep, and it’ll be refreshing [without eating into your nighttime sleepiness],” says Dr. Dasgupta. “But if your nap is longer than that, and you start going into deep sleep, it will take away from your drive to sleep that night.” Cue: the dreaded second wind.

3. You’ve accumulated sleep debt

The amount of sleep debt (aka the cumulative effect of sleep deprivation) you’ve built up can also contribute to whether you’ll experience a second wind. Generally, “the longer you’re awake, the more your brain is building up the chemicals to get you back to sleep, like adenosine,” says Dr. Kapur. So, naturally, the less sleep you get, the more tired you’ll feel.

However, according to Dr. Kennedy, the opposite effect can happen when you start stockpiling extensive sleep debt. The longer you make do with minimal sleep, the more likely it is that you put your body into “fight or flight” mode, kicking off the release of adrenaline that, paradoxically, makes you feel more alert when you want (and need) to sleep.

“If the body is sleepy or tired, and you continue to not get sleep, the nervous system will take that as a cue that there’s a reason you have to stay awake,” says Dr. Kennedy. That perception of threat is what shifts the body into survival mode, prompting the release of adrenaline and the accompanying second wind. (This is also why you might feel a temporary bump of alertness after pulling an all-nighter before you eventually crash; your body steps in to overcompensate with adrenaline, says Dr. Kennedy, as it interprets the complete lack of sleep as evidence of imminent danger.)

To be clear, there’s nothing wrong or detrimental to your health with experiencing a second wind, as long as it doesn’t interfere with your nighttime sleep. But, if that evening energy boost is significantly cutting into your ability to fall or stay asleep, devote time before bed to a soothing bedtime routine and practice good sleep hygiene (for instance, by nixing caffeine in the evening, staying away from screens before bed, and keeping your bedroom cool) to maximize your chances for a quality night of sleep—even if it begins a little later than you’d hoped.

—medically reviewed by Angela Holliday-Bell, MD