User experience (UX) is typically measured retrospectively through subjective questionnaire ratings, yet we know little of how well these retrospective ratings reflect concurrent experiences of an entire event. UX entails a broad range of dimensions of which human emotion is considered to be crucial. This paper presents an empirical study of the discrepancy between concurrent and retrospective ratings of emotions. We induced two experimental conditions of varying pleasantness. Findings show the existence of a significant discrepancy between retrospective and concurrent ratings of emotions. In the most unpleasant condition we found retrospective ratings to be significantly overestimated compared to concurrent ratings. In the most pleasant condition we found retrospective ratings to correlate with the highest and final peaks of emotional arousal. This indicates that we cannot always rely on typical retrospective UX assessments to reflect concurrent experiences. Consequently, we discuss alternative methods of assessing UX, which have considerable implications for practice.