Fatigue refers to the problem of being too tired or too exhausted.
This is common for all, which may happen at some times, but if this happens too often, then the causes of fatigue need to be understood and treatment taken.
A recent article (see-link) cites 10 causes of fatigue as follows.
Your views on the causes / effective treatment of fatigue are welcome - Dr. Sundar
http://www.webmd.com/women/guide/why-so-tired-10-causes-fatigue