Health Advice



Illness-related fatigue: More than just feeling tired

Jennifer Crystal, MFA, Harvard Health Blog on

Published in Health & Fitness

X“Tired” is a nebulous word that covers a broad spectrum of levels of fatigue. A crucial distinction, however, is between regular fatigue and illness-related fatigue.

Regular fatigue

Everyday fatigue that is not illness-related starts with a baseline of health. You may feel sleepy, you may in fact be sleep-deprived, or your body and mind may be worn out from long hours, exertion, or unrelenting stress — but you don’t feel sick. Your muscles and joints don’t ache like when you have the flu. You are capable of getting out of bed and powering through the day, even if you don’t want to. A cup of coffee or a nap might perk you up.

This type of fatigue is usually related to external factors: lack of sleep, stress, an extra-hard workout. But internally, your body is working well: your glands and organs are operating properly; infection is not depleting your body of energy; your nervous system may be overtaxed, but it’s not frayed from actual impairment.

Illness-related 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.

I felt like I had the flu, except it lasted for years. My whole body ached. I suffered migraine headaches. I had hallucinogenic nightmares. Exercise was out of the question; at times, I was literally too tired to walk up a flight of stairs or sit at the dinner table. I couldn’t concentrate, unable to read or watch TV. Sometimes I was too tired to talk.

There was no pushing through this level of fatigue, because it was caused by internal factors: illnesses that were ravaging my body. Only when they were adequately treated did I start to get my energy back.


For me, the root causes were bacterial infections (Lyme, ehrlichiosis), a parasite (babesiosis), and a virus (Epstein-Barr). Profound fatigue may also result from a host of other diseases and conditions, including chronic fatigue syndrome, fibromyalgia and multiple sclerosis.

Is it everyday fatigue or illness-related fatigue?

When determining whether your tiredness is everyday fatigue or illness-related, consider the following questions:

The bottom line

No one knows your body better than you do. You know what feels normal, and you know what you feel like when you’re sick. If you are not responding to regular fatigue remedies, your fatigue has persisted over time, you have other symptoms, or you just don’t feel right, it’s probably time to call your doctor.

(Jennifer Crystal, MFA, is a contributor to Harvard Health Publications.)

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