Objective: Earlier research on fatigue in post-COVID-19 condition (PCC) has mainly studied subjective fatigue, either over a prolonged period (trait fatigue) or in relation to a certain situation (state fatigue) in the form of perceived fatigability. Another aspect of state fatigue, cognitive performance fatigability, defined as a decline in performance over time in cognitively demanding tasks, has not been the focus of PCC research. We aimed to examine performance fatigability and the associations between these three fatigue domains. Method: Thirty-four individuals with PCC and 36 controls who recovered from COVID-19 without PCC performed cognitive tests repeated twice during the test session to assess performance fatigability. Self-reports were used to assess perceived fatigability (repeated Visual Analogue Scales) and trait fatigue (Fatigue Severity Scale, Multidimensional Fatigue Inventory). Results: Analysis of covariance showed significant interactions in two tests measuring processing speed: coding (p < .001, eta(2)(p) = .17) and a speed composite score derived from Color-Word Interference Test (p = .031, eta(2)(p) = .08), where the controls improved their performance more on the repeated tests compared with the PCC group, indicating performance fatigability in the PCC group. For the PCC group, no correlations were found between fatigue domains (r < 0.34). Conclusions: The PCC group exhibited performance fatigability in measures of processing speed. There were no correlations between fatigue domains, suggesting that the domains might represent separate constructs. The results highlight the need to differentiate between various types of fatigue in research and clinical practice and to assess performance fatigability in addition to using self-reports to obtain a comprehensive understanding of fatigue and fatigability.