causes of lethargy
Other times, lethargy can be caused by lack of exercise, alcohol use, or eating disorders. In these cases, the less you do, the more lethargic you can feel, and this can become a vicious cycle that is difficult to overcome. This could lead to disorders, such as depression or anxiety, which also have related lethargy.
Diseases of the neurological system can also cause lethargy, and examples of these include fibromyalgia and Parkinson's disease. Diseases such as these have joint discomfort or stiffness, which may cause those affected to move less. Since they cannot move well without pain, this may increase their lethargy.