Background/Objectives: Sjögren’s disease (SjD) flares are incompletely understood. The patient perspective is critical to closing this gap. This retrospective social media listening (SML) study characterized the flare lexicon within the online Reddit SjD community using novel machine learning and natural language processing. Methods: Documents (posts/comments) were analyzed from the subreddit group “r/Sjogrens” (October 2012 to August 2023). Outcomes were as follows: (1) Frequency of documents mentioning flare, and contexts in which flare was mentioned; (2) clinical concepts associated with flare (analyzed using co-occurrence and pointwise mutual information [PMI]); (3) proportion of flare vs. non-flare documents relevant to SYMPTOMS or TESTING (compared using a two-proportion z-test); and (4) primary emotions mentioned in flare documents. Results: Of 59,266 documents with 5025 authors, flare was mentioned 3330 times (4.4% of documents from 19.1% of authors). Flare was discussed as a symptom (1423 instances), disease (13), or with no clinical category (1890). Flare-associated clinical concepts (co-occurrence > 100 and PMI² > 3) included SYMPTOMS (pain, fatigue, dryness of eye, xerostomia, arthralgia, stress) and BODY PARTS (eye, mouth, joints, whole body). More flare vs. non-flare documents mentioned a SYMPTOM, whereas fewer mentioned a TEST (p < 0.001 for both). Within flare documents, 36.5% expressed emotions, primarily fear (40.5% of primary emotions), happiness (17.8%), sadness (15.7%), and anger (15.5%). Conclusions: The SjD community discusses flare frequently and in context with symptoms, specifically pain, eye and mouth dryness, and fatigue. Flare conversations frequently involve negative emotions. Additional research is required to clarify the patient experience of flare, its clinical parameters, and implications.