Identification

• Constant tiredness is a feeling of exhaustion, lethargy and weakness beyond normal fatigue. Factors leading to constant tiredness may range from medical causes such as recovering from a serious illness or medical condition to psychological reasons.
  
  

Chronic Fatigue Syndrome

• Chronic fatigue syndrome is the illness most linked with constant tiredness. Although it's not certain what causes chronic fatigue syndrome, it's often the result of having undergone a recent viral infection, usually in the upper respiratory system. This illness could have been a common cold, flu or digestive disorder causing vomiting and diarrhea.
  
  

Illnesses and Diseases

• Cancer is one of the main diseases that can cause fatigue. Heart disease can also cause constant tiredness. Other diseases and illnesses include cirrhosis, diabetes, hepatitis, multiple sclerosis, Parkinson's disease, rheumatoid arthritis and gastroesophageal reflux.
  
  

Medical Conditions

• Low blood sugar (hypoglycemia) and low pressure (hypotension) can lead to constant fatigue. Iron deficiencies (anemia) and changes in hormone levels can also be factors. An overactive thyroid gland (hyperthyroidism) or an underactive thyroid (hypothyroidism) can result in continuous tiredness. Sleep disorders such as sleep apnea can lead to constant fatigue. Fibromyalgia is a chronic condition that causes fatigue, muscle pain and tenderness, as well as stiffness in muscles, joints and tendons.
  
  

Treatments for Illnesses

• Besides battling illnesses, treating them can lead to chronic tiredness. For example, after surgery, patients sometimes need prolonged bed rest. Other treatment-induced factors may include drug treatments using medications and therapies such as antidepressants, anticonvulsants, chemotherapy and blood pressure medicines.
  
  

Psychological and Psychosocial Factors

• Psychological factors for constant fatigue may involve depression, substance abuse, eating disorders, anxiety disorders, schizophrenia, dementia and delirium. People can also suffer constant tiredness from psychosocial problems, including divorce, marital separation, poverty, bereavement and sleep disorders.
  
  

Physiological Problems

• Chronic tiredness may be caused by conditions such as pregnancy, sleep disorders or changes in work schedules. Other examples of physiological factors may include battling noises, extreme temperature and altitude conditions, overexertion and jet lag.