Fatigue is one of the most common complaints of people with chronic illness. In fact, Canadians with osteoarthritis identified reducing fatigue as a higher priority than decreasing pain. Some of this fatigue is undoubtedly due to the physiological effects of the chronic illness itself, but its pervasiveness regardless of severity of the illness leads me to believe that much—possibly most—of it comes from mental burden.

I can’t cite much evidence for this hypothesis because objective ways to measure both fatigue and mental burden are elusive. But people with chronic conditions constantly have to worry about the barriers those conditions impose and plan for contingencies, and those worries chew up energy reserves. Socially, they have to worry about being a burden to their loved ones, and, depending on the illness, they may have to worry about stigma. Another clue to the role of mental burden is how much the fatigue of chronic illness can undermine concentration.

Even when you’re “used to” a chronic condition, the worries still gnaw at the back of your mind, and, as people with episodic disabilities will attest, you don’t realize how much they weigh on you till you’re free of them.