Similarities and Differences between Fatigue and Drowsiness

Objectives.
In addressing the issue of human fatigue and decreased work capacity with the aim of reducing accident rates in specific application areas, uncertainties arise regarding fatigue and sleepiness, and whether they are identical. If not, which one should be prioritized in solving the main objective of developing a monitoring system for determining the severity of these states?
Materials and Methods.
The relationship between fatigue and sleepiness was investigated using topological modeling (TM) of complex functioning systems in the form of directed graphs, developed at Riga Technical University for computerized diagnostics tasks. The TM is a directed graph consisting of vertices and directed edges. The vertices represent functional parameters, while the edges represent cause-effect relationships between them. By applying graph theory, paths between measurable parameters and the main or code vertices of the studied states were identified. The model calculations and analysis concluded with decision-making regarding which state—fatigue or sleepiness—to focus on for developing a monitoring system.
Results.
The study demonstrates that fatigue parameters are related to energy imbalance, while sleepiness parameters are related to changes in the nervous system. The sets of parameters causing fatigue and sleepiness are distinct. Sleepiness can depend on fatigue, but not vice versa. The set of causes for sleepiness includes fatigue, but the
set of causes for fatigue does not include sleepiness.
Conclusions.
Fatigue and sleepiness are not identical concepts. Sleepiness is more dangerous than fatigue, and its measurable parameters are easier to determine, especially the extreme state of falling asleep. Fatigue does not have a distinct extreme state. The study results have enabled the development of a monitoring system that not only determines the level of sleepiness during work but also prevents falling asleep with a proactive alert system.