Your body is a fickle thing. Even when you somehow manage to resist the Instagram rabbit holes, Netflix binges, and nagging anxieties to get a full night’s sleep, it doesn’t necessarily mean you’re going to spend the next day feeling chipper. While nearly two-thirds of American adults regularly get at least seven hours of sleep, only one in seven wakes up feeling refreshed every day of the week. What’s more, 45 percent of those getting seven to eight hours a night still feel fatigued as many as three days a week. On the other hand, there are those weird days where you’ve spent the night tossing and turning, get out of bed in the morning expecting to feel like a zombie, and … actually feel pretty okay. Normal, even.
The reason is that tiredness is complex: the relationship between sleep and energy level is less one-to-one than you might believe. In fact, fatigue is defined as a “nonspecific symptom,” meaning it can arise from many causes.
And so can the lack thereof. If the workday after a sleepless night feels like any other day, there are a few different explanations for your mysterious alertness — and understanding them can help you the next time around. Here are a few questions to ask yourself the next time you find yourself riding an unearned wave of energy (or, conversely, when you feel yourself dragging after a good night’s sleep).
What did I have for breakfast?
Was it an omelette? Some peanut butter toast? A Greek yogurt? A high-protein morning meal will keep you alert much longer than something like a pastry — protein regulates your energy levels, keeping them strong and steady throughout the day.
Which means you should probably fight the urge to grab a muffin or some other carb-laden snack for your afternoon pick-me-up. Studies have shown that we’re more likely to choose carbohydrate-heavy foods when we’re drowsy, because our bodies know they’re easier to digest and offer a quicker path to an energy boost. But those boosts are temporary and backfire relatively quickly — your blood sugar will spike and then drop, resulting in the dreaded carb coma. If you can stick to protein-rich meals for most of the day, reward yourself with a starchy dinner and an early bedtime. You’ve earned it.
Just don’t eat those carbs too late at night. “Eating close to bedtime can really mess up your sleep, and also give you reflux,” says Cynthia Seely, a sleep and dreams researcher based in Seattle. Unless you want to have another rough night’s sleep, time that bowl of pasta for around three or four hours before calling it a night.
Have I been moving?
Light to moderate exercise improves sleep quality, as well as your perceived energy levels during the day. This doesn’t have to mean hitting then gym, either — something as low-key as walking briskly to the subway, or doing some YouTube-guided yoga before you leave for work, could have the same effect. You don’t need to go for a run or lift a bunch of weights; in fact, the accompanying physical fatigue might be less effective.
And ideally, you’ll find ways to keep yourself moving throughout the day. Even someone who got a full eight hours of rest might struggle to stay awake through a long meeting — though sitting for long periods of time doesn’t seem like it would tire you out, it can be every bit as fatiguing as more strenuous activity. Sitting puts our bodies on pause in a few different ways: Number one, your body stops producing lipase, an enzyme that gets energy from our body fat, so you have less access to your body’s natural energy. Number two, your heart rate slows, which in turn slows down your nervous system and breathing. Prolonged sitting also won’t wear out your muscles, so it doesn’t correlate with better sleep the way exercise does. Instead, you might sleep poorly because you haven’t moved much, leading to a vicious cycle of daytime sleepiness and nighttime wakefulness.
How many things do I have on my plate?
This one is a bit of a double-edged sword. On the one hand, stress often seems to make people more alert, because it’s because the body’s way of functioning in the face of obstacles that might otherwise put it out of commission. “[Say] there’s something really stressful where you just have to function regardless,” Seely says. “I think you can do that for a period of time.” If you sit down at your desk, glance at your to-do list, and notice that you feel wide awake, this might be why.
But stress can only keep the body going for so long, and because the body is putting forth more energy than it has in the bank, sooner or later, a stress-induced high will necessitate an equal and opposite low. Or, as Seely puts it, “At some point, you’re going to crash.” Plus, high stress levels can lower your sleep quality, which will add to your fatigue without your knowing it. (By the way, if you are one of those strange people who falls asleep as a response to severe stress, here’s why.)
On the flip side, fatigue can set in when the mind is understimulated. The solution to boredom-induced tiredness is similar to the one for sitting —find gentle ways to stimulate your brain that don’t take up too much of your mental energy. So if you’re nodding off on a long car ride, for example, put on upbeat music; if you’re starting to doze off in class, try doodling.
Is anyone I love mad at me?
Relationships can be huge contributors to stress, Seely says. Particularly because many people sleep next to their partners, inter-relationship tension can drain reserves throughout the day and night.
In this case, fatigue can be helpful — after all, it’s a warning sign that you’re dealing with a larger problem. It might be a stretch to say you can measure your relationship’s health using your own tiredness as a barometer, but the extra data point can’t hurt.