ObjectivesThis study aimed to produce a patient-centered understanding of mental health symptoms of people with the post-COVID-19 syndrome (PCS).MethodsA cross-sectional analysis of 414 participants in a longitudinal study was carried out involving people who self-identified as having symptoms of PCS. People were asked to name their most frequent and most bothersome mental health symptoms affected by PCS using the structure of the Patient Generated Index (PGI). The text threads from the PGI were grouped into topics using BERTopic analysis.Results20 topics were identified from 818 text threads referring to PCS mental health symptoms. 35% of threads were identified as relating to anxiety, discussed in terms of five topics: generalized/social anxiety, fear/worry, post-traumatic stress, panic, and nervous. 29% of threads were identified as relating to low mood, represented by five topics: depression, discouragement, emotional distress, sadness, and loneliness. A cognitive domain (22% of threads) was covered by four topics referring to concentration, memory, brain fog, and mental fatigue. Topics related to frustration, anger, irritability. and mood swings (7%) were considered as one domain and there were separate topics related to motivation, insomnia, and isolation.ConclusionsThis novel method of digital transformation of unstructured text data uncovered different ways in which people think about classical mental health domains. This information could be used to evaluate whether existing measures cover the content identified by people with PCS, to initiate a clinical conversation, or to justify the development of a new measure of the mental health impact of PCS. Why is this study needed?The symptoms of infection with the COVID-19 virus can last a very long time and this situation has been called the post-COVID syndrome (PCS) or long COVID. PCS is a poorly understood condition with symptoms affecting all body systems with both primary and secondary effects on mental health.What is the key problem/issue/question this manuscript addresses?A long time ago, a famous scientist (Lord Kelvin) said you can't fix what you can't measure, and you can't measure what you don't understand. This study is about starting the understanding part of the mental health consequences of PCS.What is the main point of your study?The main point of the study was to ascertain directly from people with PCS, in their own words, their most distressing mental health symptoms. This was preferred to asking people to fill out questionnaires on mental health symptoms that used fixed questions that were not developed for people with PCS.What are your main results and what do they mean?Anxiety and depression were the most common mental health effects and each was expressed in five different ways; cognitive problems were also common and expressed four different ways. People also identified experiencing frustration, anger, irritability, mood swings, apathy, insomnia, and isolation showing that PCS has very diverse effects not easily described using standard questionnaires.