Feeling tired or fatigued is a common experience. Yet health-care providers often dismiss complaints about tiredness - both because the symptom is universal and because it can be challenging to evaluate medically, says Michael Grandner, director of the University of Arizona's Sleep & Health Research Program in Tucson.
And while tiredness is often temporary, treatable or nothing to worry about, experts say that tiredness that suddenly worsens or prevents you from doing what you want can be a sign of a health problem or sleep disorder.
"Sleep seems to be a canary in the coal mine, where it's sensitive to all these things going on in your body," Grandner says.
"So, when it starts changing, you want to ask, 'Well, what's going on?'"
Sleepiness, fatigue, tiredness: in conversation, people use the terms interchangeably. But medically, their definitions differ. Understanding the differences is an important first step toward tackling the problem - or figuring out if there is one.
Sleepiness is a need for sleep that makes it difficult to stay awake, even while driving, working or watching a movie, and even after ingesting caffeine.
Fatigue, on the other hand, is a deeper sort of an inability, either physical or mental, to do what you want to do, such as get to the grocery store.
Somewhere in the middle is tiredness, a desire to rest that is less debilitating than fatigue and less dramatic than sleepiness. You can still be productive while tired.
Whatever you call it, it's common. In a 2014 survey by the nonprofit National Sleep Foundation, 45 percent of adults said they had been affected by poor sleep or not enough sleep in the previous week.
As many as 20 percent of people report excessive sleepiness on a regular basis. And, a National Safety Council survey reported in 2017 that 76 percent of people felt tired at work.