Background: Functional neurological disorder (FND) is one of the commonest conditions in neurological practice, describing symptoms like paralysis and seizures that can be severe and disabling. It is a diagnosis that is confirmed clinically rather than by scans or laboratory results. It is a stigmatized and widely misperceived condition, and since the emergence of long COVID, there has been some conflation of FND with other conditions, which has caused further misunderstanding. Social media has become increasingly popular for patients to learn and interact about their conditions, and the information that they seek and receive may be shaped by many factors. Prior to this study, the online discourse about FND had not been described in the literature. Objective: We aimed to analyze and describe how FND is discussed on the social media platform X (formerly known as Twitter) using a mixed methods approach. Methods: Using search terms related to FND, the authors collected data from 426 users and 1104 posts, generating a total of 7640 replies and reposts over a 2-month time frame in 2024. Quantitative descriptive and social network analyses were carried out to map key influential users and communities, in addition to measuring the influence of users. Content analysis was undertaken to describe the prevalent topics being discussed. Results: More users overall associated with conditions outside FND (n=180, 42.3%), mostly long COVID and myalgic encephalomyelitis/chronic fatigue syndrome, compared with FND (n=148, 34.7%). Self-declared patients made up 40.8% (450/1104) of posts and 36.4% (n=155) of users. Social network analysis revealed 2 separate communities with little interaction. There was a prominence of myalgic encephalomyelitis/chronic fatigue syndrome and long COVID–associated users (nodes) over FND users (nodes). The former cluster showed stronger connections outwardly or peripherally than the FND cluster, suggesting that they may have a stronger impact on shaping the public narrative around FND than FND nodes. In total, 7 of the top 10 most influential users often displayed anti-FND views, while FND organizations and professionals had much less influence. There were 58 posts with at least 5000 views. Of these 58, 10 were from self-declared FND professionals, while 19 were from self-declared professionals associated with other conditions. Of these highly viewed posts, 38 of 58 were negatively predisposed toward FND. Content analysis showed themes of (1) conflict, (2) deception, (3) mistreatment and harm, (4) symptom experience, (5) knowledge, and (6) support. Conclusions: A large proportion of the discourse around FND on X is shaped by users who are dismissive of the concept of FND and those associated with it. These findings have implications for individuals getting support for a condition that is already widely misunderstood. This study could provide a template for assessing how other stigmatized conditions are perceived on the web. Trial Registration: