What is Fatigue?

Fatigue 

Definition
By Mayo Clinic Staff
Nearly everyone struggles with being overtired or overworked from time to time. Such instances of temporary fatigue usually have an identifiable cause and a likely remedy.
Chronic fatigue, on the other hand, lasts longer and is more profound. It's a nearly constant state of weariness that develops over time and diminishes your energy and mental capacity. Fatigue at this level impacts your emotional and psychological well-being, too.
Fatigue isn't the same thing as sleepiness, although it's often accompanied by a desire to sleep — and a lack of motivation to do anything else.
In some cases, fatigue is a symptom of an underlying medical problem that requires medical treatment. Most of the time, however, fatigue can be traced to one or more of your habits or routines.
Causes
Taking a quick inventory of the things that might be responsible for your fatigue is the first step toward relief. In general, most cases of fatigue may be attributed to three areas: lifestyle factors, medical conditions or psychological problems.
Lifestyle factors
Feelings of fatigue often have an obvious cause, such as:
Alcohol use or abuse
Caffeine use
Excessive physical activity
Inactivity
Lack of sleep
Medications, such as antihistamines, cough medicines and cold remedies
Unhealthy eating habits
Psychological conditions
Fatigue is a common symptom of mental health problems, such as:

Anxiety
Depression
Grief
Stress
Medical conditions
Unrelenting exhaustion may be a sign of a medical condition or underlying illness, such as:
Acute liver failure
Anemia
Cancer
Chronic fatigue syndrome
Chronic kidney disease
COPD
Emphysema
Heart disease
Hyperthyroidism (overactive thyroid)
Hypothyroidism (underactive thyroid)
Medications, such as prescription pain medications, heart medications, blood pressure medications and some antidepressants
Obesity
Restless legs syndrome
Sleep apnea
Type 1 diabetes
Type 2 diabetes