Do you always feel tired? Do you often have difficulty getting through the day because of lack of energy? Sometimes, being tired is expected and normal (such as after an all-nighter, a bout of the flu, or a busy non-stop week). However, if you find yourself always feeling fatigued and worn out despite adequate rest, to the point your tiredness negatively affects your quality of life, it’s time to do something about it. In this article, I will discuss six causes of fatigue and daytime sleepiness that—while common and treatable—often goes undiagnosed. In another article, I discuss practical ways in which you can fight fatigue and improve your energy level.