Background: Compared with adults in the general population, autistic adults are more likely to experience poor mental health, which can contribute to increased suicidality. While the autistic community has long identified autistic burnout as a significant mental health risk, to date, only one study has been published. Early research has highlighted the harmful impact of autistic burnout among autistic adults and the urgent need to better understand this phenomenon. Methods: To understand the lived experiences of autistic adults, we used data scraping to extract public posts about autistic burnout from 2 online platforms shared between 2005 and 2019, which yielded 1127 posts. Using reflexive thematic analysis and an inductive ''bottom-up'' approach, we sought to understand the etiology, symptoms, and impact of autistic burnout, as well as prevention and recovery strategies. Two autistic researchers with self-reported experience of autistic burnout reviewed the themes and provided insight and feedback. Results: We identified eight primary themes and three subthemes across the data. (1) Systemic, pervasive lack of autism awareness. (1.1) Discrimination and stigma. (2) A chronic or recurrent condition. (3) Direct impact on health and well-being. (4) A life unlived. (5) A blessing in disguise? (6) Self-awareness and personal control influence risk. (6.1) ''You need enough balloons to manage the weight of the rocks.'' (7) Masking: Damned if you do, damned if you don't. (8) Ask the experts. (8.1) Stronger together. The overarching theme was that a pervasive lack of awareness and stigma about autism underlie autistic burnout. Conclusions: We identified a set of distinct yet interrelated factors that characterize autistic burnout as a recurring condition that can, directly and indirectly, impact autistic people's functioning, mental health, quality of life, and well-being. The findings suggest that increased awareness and acceptance of autism could be key to burnout prevention and recovery.