Many different illnesses and mental health conditions can cause fatigue and drowsiness, also known as lethargy. Medications, extreme physical exertion, and sleep disruptions are also common causes, as are lifestyle factors, such as a poor diet. While most causes of lethargy are not dangerous, it can sometimes indicate a severe illness.

Medical Causes

Drowsiness and fatigue can be the result of many chronic or temporary medical conditions. Thyroid problems, such as hypothyroidism, can slow the metabolism and may result in exhaustion or weekness. Organ disorders, like jaundice, are also associated with lethargy. Common illnesses, such as a cold, food poisoning, or the flu, can also result in days or weeks of feeling run down and tired as the body puts its energy into fighting off the infection.

Treating Medical Causes

Curing lethargy caused by illness is usually a matter of diagnosing and treating the underlying cause. If fatigue is due to a common illness, it will typically pass in a few weeks. More serious conditions may need to be treated with medication or harmone therapy. Some causes of fatigue are very hard to treat, and patients may need to make lifestyle changes in order to manage the conditions effectively.

Psychological Factors

When psychological disorders are involved, lethargy may be accompanied by feelings of indifference or detachment, as well as exhaustion. For some people, the symptoms come and go, while others experience constant drowsiness or mental fatigue. The condition is often related to depression or bipolar disorder. In acute cases, it may also be a symptom of shock.

Treating Psychological Causes

Psychological causes of fatigue or indifference can be treated in a variety of ways, depending on the specific cause. Some type of psychotherapy may be helpful, as can making behavioral changes, but this might not be enough on its own. A health care professional may prescribe medications that can correct chemical imbalances in the brain if this is believed to be part of the cause.

Reasons for Lethargy

  • Coeliac disease
  •  anaemia
  • Chronic fatigue syndrome
  • Sleep apnoea
  • underactive thyroid
  • diabetes
  • Glandular fever
  • depression
  • Restless legs
  • Anxiety