Startled awake by an alarm, half asleep, desperate for coffee -- that describes at least half of all Americans, who wake up not feeling rested.

But when does that tired feeling mean something else is wrong? Being tired – the sandy eyes and foggy head – has a more worrying cousin, fatigue, which is more severe and can be linked to illness.

The Long Days

There’s nothing wrong with feeling tired, especially now, with parents working at home and helping their kids with remote learning. Bloomberg News anecdotally reports that people may be doing as many as three extra hours of work a day. It’s no wonder we’re ready for a nap.

A Full 8 Hours

Of course, over time, lack of sleep for any reason can be a problem. The National Institutes of Health mentions the possibility of accidents when people are sleep deprived. Lack of sleep can disrupt memory formation and change cognition.

Fatigue, however, is different and can the symptom of an illness. Jennifer Crystal, a contributor to Harvard Health Publishing, described her battle with Lyme disease in a story on fatigue:

“When I was acutely ill with persistent Lyme, babesiosis and ehrlichiosis (all tick-borne illnesses), as well as chronic Epstein-Barr virus, a good night’s sleep did nothing. Naps were staples of my day that helped me survive but didn’t improve my energy. Drinking a cup of coffee was akin to treating an ear infection with candy. No matter how much I rested, my exhaustion persisted.”

But What’s the Difference?

Tiredness, Ms. Crystal said, can be fixed with a nap or a cup of coffee (or better sleep habits). Fatigue might feel like the flu, with aches and chills, and could get worse as the week goes on.

An overview of fatigue published in the American Family Physician explained that, while fatigue can be a psychological condition and some people benefit from cognitive behavioral therapy, it can also result from anemia, cancer, depression, viral infection and other types of infection.

Counterintuitively, many persons who suffer fatigue can benefit from exercise. Stimulants like caffeine are less effective but could still be useful.

The take-home

The bottom line for people who are either chronically tired or chronically fatigued is to talk with a doctor. For those who are tired, a doctor can help strategize better sleeping habits and lifestyle changes to fix the issue. For people who are fatigued, seeing a doctor is essential to rule out an underlying condition and help you get back to a full life.

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Sabrina Emms is a science journalist. She got her start as an intern at a health and science podcast out of Philadelphia public radio. Before that she worked as a researcher, looking at the way bones are formed. When out of the lab and away from her computer, she's moonlighted as a pig vet's assistant and a bagel baker.