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An analysis of more than 554,000 posts from online narcolepsy and idiopathic hypersomnia communities found that patients commonly linked “brain fog” to memory problems, forgetfulness and difficulty concentrating. The researchers said the term appeared distinct from fatigue and sleepiness, while noting that the findings reflect self-selected online communities, not population-wide rates.
A social media analysis of 554,312 posts and comments from online communities for people with narcolepsy and idiopathic hypersomnia found that users most often described “brain fog” through memory and concentration problems, rather than using it only as another term for fatigue. Researchers presented the findings at the Neuroscience Education Institute (NEI) Fall Congress in Colorado Springs, offering a patient-language perspective on a symptom that has no agreed definition.
Researchers examined posts from the Reddit communities r/Narcolepsy and r/idiopathichypersomnia, as well as the Facebook group PWN4PWN, dating from August 2011 to September 2025. About 85% of the material came from r/Narcolepsy. The team used semantic similarity analysis to identify words and experiences associated with “brain fog.”
The leading related terms included forgetfulness, memory, fatigue, drunkenness and dissociation. Other closely associated descriptions included tiredness, difficulty concentrating, inability to focus, poor memory and memory issues. When researchers grouped clinical experiences, memory-related terms and impaired concentration again featured prominently, alongside fatigue and forgetfulness.
The analysis also compared people’s descriptions according to whether their posts emphasized fatigue, sleepiness, or a balance between the two. The sharpest difference was between users whose descriptions gave similar weight to fatigue and sleepiness and those whose posts emphasized sleepiness much more. The balanced group more often linked brain fog to memory and focus; the very sleepiness-dominant group more often connected it with energy and motivation, sometimes describing it as constant, intense or severe.
Why Patient Language Matters
The findings suggest that asking only about fatigue or daytime sleepiness may not capture how some patients experience cognitive difficulties. Study author Anne Marie Morse, DO, of Geisinger Medical Center, told MedPage Today that clinicians should ask patients to explain brain fog in their own words and treat it as a symptom in its own right, while recognizing that fatigue and sleepiness can affect its severity.
That distinction may matter in daily life. Morse said patients describe cognitive effects that can interfere with school, work, driving and family participation. The analysis does not establish how common these effects are across all people with sleep disorders, but it points to questions that standard measures focused on sleepiness might not answer.
The researchers also said a stable, shared vocabulary could help inform a patient-reported outcome measure—a way of recording symptoms using language that reflects patients’ own accounts. Such a measure could support future research into how brain fog changes and how it relates to other symptoms, though the analysis itself did not validate a new clinical tool.
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How Brain Fog Was Described
Morse told MedPage Today that there is no agreed definition of brain fog or consensus on whether patients with different conditions experience it in the same way. She said clinical conversations can be shaped by the setting, which led the researchers to examine unprompted descriptions in online communities.
The report also places the term in a longer timeline. According to Morse, an earlier social listening analysis found that use of “brain fog” predated COVID-related discussion by at least a decade, while its use grew afterward alongside research into conditions including celiac disease and fibromyalgia. In this analysis, mentions rose each year from 2011 to 2017, then stayed at about 1% of all posts through 2025. The researchers described the meaning as largely consistent from 2018 onward, following an earlier shift in descriptors from memory toward exhaustion and tiredness.
““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, speaking to MedPage Today
Limits of the Online Evidence
The findings describe language used in selected online communities, not the prevalence of brain fog among all people with narcolepsy or idiopathic hypersomnia. Morse identified self-selection as a limitation: people who post in these groups may not represent the broader patient population, and the analysis captures conversational patterns rather than population estimates.
Researchers also could not independently verify participants’ clinical diagnoses from social media posts. The analysis shows which terms appeared in association with brain fog, but it does not establish that one symptom causes another, measure how severe symptoms are for patients generally, or determine whether the patterns apply to other conditions.
From Online Terms to Clinical Measures
The study’s proposed next step is to explore whether patients’ recurring descriptions can support a patient-reported measure of brain fog. The conference findings do not establish that such a tool has been developed or tested. Further work would need to assess whether the language identified online is useful and reliable when gathered directly from patients in clinical or research settings.
For now, Morse’s practical recommendation is that clinicians ask patients specifically what they mean by brain fog and record the answer without automatically substituting fatigue or sleepiness. Whether that approach improves symptom tracking or patient outcomes was not assessed in this social media analysis.
Key Questions
What did people in the analysis mean by “brain fog”?
Posts commonly connected it with memory problems, forgetfulness and difficulty concentrating. Fatigue also appeared among the associated terms, but researchers said the wider pattern suggested brain fog was not simply another word for tiredness.
Which sleep disorders did the study examine?
The posts came from online communities focused on narcolepsy and idiopathic hypersomnia. The researchers did not independently confirm diagnoses reported by social media users.
Does the study show how common brain fog is among patients?
No. The analysis measured language in selected online communities and cannot establish how prevalent brain fog is among all people with these disorders. Its authors also noted that people who post online may not represent the broader patient population.
What did the researchers recommend clinicians do?
Morse recommended asking patients to describe brain fog in their own words and treating it as a separate symptom, rather than assuming it means fatigue or sleepiness. The study did not test whether this approach changes care or outcomes.
Source: medpagetoday.com
