What is a principal cause of daytime fatigue?

Daytime fatigue can often be traced back to a lack of sleep, which is a fundamental requirement for overall health and energy levels. Adequate sleep allows the body to repair itself, process information, and rejuvenate both physically and mentally. When someone does not get enough restful sleep, it leads to increased feelings of tiredness and fatigue during daytime activities.

While the other options like excessive physical activity, lack of water, and poor nutrition can contribute to feelings of fatigue, they are typically secondary factors when it comes to the principal cause. For instance, excessive physical activity without proper recovery can lead to fatigue, but it is usually the lack of restorative sleep that exacerbates the tiredness. Similarly, while dehydration and poor nutrition can diminish energy levels, they often stem from or are worsened by inadequate rest. Therefore, lack of sleep is a significant driver of daytime fatigue, making it the most crucial factor in this context.