When you're feeling exhausted, the first advice is always to get more sleep.
It makes sense that you're nodding off in the afternoons if long work hours or a screaming toddler are interfering with your rest.
But some of us spend our days tired and lethargic even after getting the recommended 7+ hours of shut-eye every night. So, what's going on?
As this episode of AsapSCIENCE explains, there's a wide range of reasons you could be constantly fatigued even if you think you're getting enough sleep:
For starters, you might just be too sedentary.
Even though we think of physical exertion as exhausting, it turns out that doing light exercise just a few times a week can leave you more energised.
Just think back to a time when you've had an unusually active day outdoors, maybe going on a hike or throwing frisbee in the park.
Chances are you slept exceptionally well that night. People who exercise regularly get to enjoy a better night's sleep, even if the number of hours they sleep remains the same.
Another common trap is our reliance on caffeine to stay awake.
Even though most of us wouldn't guzzle espresso straight before bed, the window for avoiding caffeine is actually much longer.
Caffeine blocks adenosine, a neurotransmitter that accumulates in the brain throughout the day, making us drowsy in the evenings.
If you have coffee even as early as six hours before bed, it will mess with your adenosine production, making it harder to go to sleep.
Besides, studies have shown that caffeine actually messes with our circadian rhythms.
But sometimes your exhaustion is not down to simple lifestyle choices, and instead is related to mental health, the video above explains.
For example, generalised anxiety disorder can come with fatigue, and even just high levels of stress and worrying will leave you pretty drained.
Depression comes with an impact on quality of sleep as well, even causing insomnia in some cases.
Apart from mental health, physical conditions can also cause excessive tiredness. Those are best left to be diagnosed by your doctor, but include such things as iron deficiency, thyroid problems and diabetes.
So, there's really no one quick solution for dealing with constant fatigue, but at least AsapSCIENCE gives you a handy checklist of things to look out for.
A lot of their advice - like the tip about exercise - is pretty easy to take on board, unless you are dealing with 'social jetlag', which we'll let the video explain in detail.
Maybe you're just one of those people not built for a 9-5 lifestyle, in which case we're sorry.
Here, have a coffee nap.
A version of this article was first published in April 2017.