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A social media analysis of 554,312 posts and comments in narcolepsy and idiopathic hypersomnia communities found that patients commonly associated brain fog with memory problems and difficulty concentrating, not only fatigue. The findings, presented at the NEI Fall Congress, may help researchers and clinicians measure and discuss the symptom, but online posts cannot establish how common it is among all patients.
A lexicon analysis of 554,312 posts and comments from online communities for narcolepsy and idiopathic hypersomnia found that people often describe brain fog through memory problems, forgetfulness and difficulty concentrating—not simply as fatigue or sleepiness. The findings, presented at the Neuroscience Education Institute (NEI) Fall Congress in Colorado Springs, could help shape how clinicians ask about the symptom and how researchers develop patient-reported measures.
Researchers examined posts from the Reddit communities r/Narcolepsy and r/idiopathichypersomnia and the Facebook group PWN4PWN, spanning August 2011 through September 2025. About 85% of the material came from r/Narcolepsy. Using semantic similarity to identify words used in related contexts, the team found associations including “forgetfulness,” “memory,” “fatigue,” “drunkenness” and “dissociation.” Other closely related descriptions included difficulty concentrating, inability to focus, poor memory and memory issues.
The analysis also identified differences in how people used the term depending on whether their posts emphasized fatigue or sleepiness. Those whose descriptions were more balanced between the two tended to connect brain fog with memory and focus. People in the very sleepiness-dominant group more often linked it with energy and motivation, and used intensity or duration terms such as “constant,” “intense” and “severe.” The researchers divided posts mentioning fatigue or sleepiness into four groups for this comparison.
Anne Marie Morse, DO, of Geisinger Medical Center, and colleagues reported that mentions of brain fog rose each year from 2011 to 2017, then remained at about 1% of posts through 2025. The study found some shifts in associated language over time, including a move from memory-focused descriptions toward exhaustion and tiredness between the earlier periods studied. The vocabulary was relatively consistent from 2018 through 2025, according to the report.
Why Patient Language Matters
The findings matter because brain fog is a patient-reported experience without an agreed definition, and a general measure of sleepiness may not capture its cognitive aspects. If clinicians treat a patient’s description as interchangeable with fatigue, they may miss concerns about memory, concentration or day-to-day functioning. Morse advised clinicians to ask patients what they mean by brain fog and to consider it as its own symptom, while recognizing that fatigue or sleepiness may occur alongside it.
The analysis also points to a possible research use: a stable vocabulary shared in patient communities could inform a patient-reported outcome measure built around patients’ own descriptions. Such a measure could help researchers track the symptom more directly. The study does not establish that the words found online represent every patient’s experience, nor does it show that a new measure has been developed or validated.
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How Researchers Read Online Posts
Morse told MedPage Today that researchers wanted to understand how people with narcolepsy type 1, narcolepsy type 2 and idiopathic hypersomnia described brain fog without being prompted in a clinical or research encounter. She said an earlier social listening analysis found that use of the phrase predated COVID-19 by at least a decade, although its use grew afterward alongside research into brain fog across conditions.
For this analysis, the team used semantic similarity, calculated with cosine similarity, to identify words and clinical experiences associated with the phrase. The researchers also compared language across groups defined by the relative prominence of fatigue and sleepiness in posts. These methods describe patterns in the collected text; they do not independently confirm a poster’s diagnosis or measure symptoms through clinical assessments.
““Brain fog” is one of the most burdensome symptoms people with narcolepsy and idiopathic hypersomnia experience, but there is no agreed definition of what it means.”
— Anne Marie Morse, DO, of Geisinger Medical Center, speaking to MedPage Today
Limits of the Online Evidence
The posts came from self-selected online communities, so the results reflect how participants talk about brain fog there, not its prevalence among all people with narcolepsy or idiopathic hypersomnia. The researchers also could not independently verify users’ clinical diagnoses from social media data. The findings therefore show language patterns, not a population-wide estimate or proof that every patient uses the term in the same way.
It is also unclear from the report whether the proposed patient-reported measure will be developed, how it would be tested, or whether the observed differences between fatigue and sleepiness groups would hold in a clinically assessed sample. The analysis does not establish the cause of brain fog or determine how it should be treated.
Next Steps for Research and Care
Morse said the stability of the vocabulary could support work on a patient-reported measure that uses language drawn from people living with these conditions. Researchers would need to develop and validate such a measure before it could be relied on as a clinical or research endpoint. The conference report does not provide a timeline for that work.
For now, Morse’s practical recommendation is for clinicians to ask patients to describe brain fog in their own words and discuss it separately from sleepiness and fatigue. Whether those conversations or a future measure improve assessment has not been tested by this social media analysis.
Key Questions
What did the analysis find patients mean by brain fog?
In the posts analyzed, brain fog was commonly associated with memory impairment, forgetfulness and difficulty concentrating. Other associated descriptions included fatigue, poor memory and inability to focus.
Was brain fog described only as fatigue or sleepiness?
No. The analysis found that fatigue and sleepiness appeared in the language, but memory and concentration were also prominent. The researchers reported different patterns across groups whose posts emphasized fatigue or sleepiness to varying degrees.
Who took part in the study?
The study analyzed posts and comments from two Reddit communities—r/Narcolepsy and r/idiopathichypersomnia—and the Facebook group PWN4PWN. The researchers could not independently confirm users’ diagnoses.
Can the results show how common brain fog is among patients?
No. The data came from self-selected online communities and show how participants used language there. They do not provide a reliable estimate of how common brain fog is across all people with narcolepsy or idiopathic hypersomnia.
What did the researchers suggest clinicians do?
Morse recommended asking patients what brain fog means to them and treating the answer as a distinct symptom rather than translating it automatically into fatigue or sleepiness. Those symptoms can occur alongside it.
Source: medpagetoday.com
