Using social network services is associated with positive outcomes for users. However, negative user experiences can also be present as part of use. Fatigue and overload have become common phenomena that harmfully impact users' well-being as well as the business of such services. Antecedents of fatigue such as information, communication and system feature overload have been studied in the literature but it was unknown how users evaluate situations where fatigue and overload are present. The aim of this thesis was to study how users evaluate situations that induce fatigue and overload in the context of social network services. Processing fluency was selected as a guiding framework since it is one of the most significant metacognitive cues used in evaluating situations. The study was conducted online via Zoom and focused on Facebook out of social network services. In the quasi-experimental portion of the study, participants performed six tasks in Facebook and the speed and accuracy of these tasks were measured as equivalents of processing fluency. Processing fluency as a subjective metric was measured in a survey. 28 people participated in the study. The objective metric of fluency was sensitive to uncontrolled factors in the study and thus no correlations were found in the statistical analysis. However, in the results a negative correlation was found between processing fluency as measured with a subjective metric and system feature overload as well as general overload. Subjective fluency did not correlate with fatigue but the connection could be indirect where fluency is connected to fatigue through overload. The study contributes to present literature by showing that cognitive phenomena such as processing fluency are associated with the evaluation of situations where fatigue and overload arise. This means preventing and decreasing the impact of fatigue and overload could possibly benefit from taking processing fluency into account as part of user experience. Examining the causality between processing fluency and overload more closely and quantifying the results in a social network service other than Facebook are some of the directions future studies could take.