'What Do Patients With Sleep Disorder Really Mean by 'Brain Fog'?'

 Brain fog among individuals with sleep disorders was primarily characterized by memory impairment, difficulty concentrating, and forgetfulness, according to a lexicon analysis of social media posts.

Among 554,312 posts and comments in online narcolepsy and idiopathic hypersomnia communities, the top five contextual words associated with brain fog -- unrelated to symptom relief -- were "forgetfulness," "memory," "fatigue," "drunkenness," and "dissociation."

Meanwhile, some of the most common terms associated with symptom alleviation were "clears," "lifted," "lifts," and "clearing," reported Anne Marie Morse, DO, of Geisinger Medical Center in Danville, Pennsylvania, and colleagues.

The findings were presented at the Neuroscience Education Institute (NEI) Fall Congress in Colorado Springs, Colorado.

"'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, whether patients experience the same thing, or specifically whether it varies by condition," Morse told MedPage Today. "Anything we think we know about brain fog comes from clinical or research encounters, where the conversation is already conditioned or biased by the setting."

"In a prior social listening analysis, we evaluated the term's use over time to challenge the idea that this was merely popularized by COVID-related brain fog," she continued. "We found that the term predated COVID by at least a decade, though use grew significantly thereafter alongside research across conditions like celiac disease and fibromyalgia. We wanted to understand how people living with narcolepsy type 1, narcolepsy type 2, and idiopathic hypersomnia describe it on their own, unprompted."

For the social listening analysis, researchers evaluated posts and comments from two subreddits (r/Narcolepsy and r/idiopathichypersomnia) and one Facebook group (PWN4PWN) between August 2011 and September 2025. Most data (85%) originated from r/Narcolepsy. Semantic similarity was calculated using cosine similarity.

The top five non-synonymous terms with the highest semantic similarity to brain fog were "tiredness," "difficulty concentrating," "inability to focus," "poor memory," and "memory issues." Additionally, the top five associated clinical experiences were led by memory-related symptoms and included "impaired memory," "memory dysfunction," "impaired concentration," "fatigue," and "forgetful."

To assess how fatigue and sleepiness influence the meaning of brain fog, authors mentioning either symptom were stratified into four cohorts: fatigue-dominant, sleepiness-dominant (sleepiness exceeded fatigue by <7.5%), very sleepiness-dominant (sleepiness exceeded fatigue by ≥7.5%), and fatigue/sleepiness-balanced.

When comparing the groups, the greatest discrepancy in how brain fog was characterized occurred between the fatigue/sleepiness-balanced and very sleepiness-dominant groups. Authors in the balanced cohort tended to frame brain fog around memory and focus connotations, whereas those in the very sleepiness-dominant group connected the term to energy and motivation, frequently pairing it with time and intensity qualifiers such as "constant," "intense," and "severe."

Morse emphasized that brain fog is not simply a synonym for fatigue or sleepiness. "In the community data, [brain fog] separates out as its own concept, and its meaning has been stable since 2018, which suggests a mature shared vocabulary rather than a passing phrase," she said.

Mentions of brain fog increased annually from 2011 to 2017 before stabilizing at approximately 1% of all posts through 2025. Semantic shifts were subtle, with the most notable transition occurring between 2011 to 2017 and 2018 to 2020, when descriptors shifted away from memory-focused terms toward exhaustion and tiredness. Meaning remained consistent from 2018 through 2025.

"The stability of this vocabulary may potentially be valuable for research," Morse noted. "If people with these conditions use 'brain fog' consistently with the same personal meaning across years and communities, that supports building a patient-reported outcome measure using their language instead of ours, establishing clinical endpoints that reflect what they actually experience."

For practicing clinicians, Morse recommended asking patients about brain fog in their own words. "Treat the answer as its own symptom. Don't translate it into fatigue or sleepiness, although concurrent fatigue or sleepiness may modify the severity of brain fog."

"Patients are telling us that cognition is a core part of how this condition costs them their day -- at school, at work, driving, and being present with family. We must start asking about it specifically rather than relying on a guesstimate from a sleepiness score or missing the discussion entirely," she said.

Morse also noted two key study limitations: online communities are self-selected, reflecting conversational patterns rather than true population prevalence, and clinical diagnoses cannot be independently verified from social media data.

Disclosures

The study was funded by Avadel Pharmaceuticals, an affiliate of Alkermes.

Morse disclosed relationships with Alkermes, Apnimed, Avadel Pharmaceuticals, Axsome Therapeutics, Eisai, Harmony Biosciences, Jazz Pharmaceuticals, Eli Lilly, Lundbeck, Noble Pharmaceuticals, Novartis, Takeda Pharmaceutical, the NIH, UCB Pharmaceuticals, ResMed Foundation, Coverys Community Healthcare Foundation, Geisinger Health Plan, DAMM Good Sleep, NanoMosaic, Neura Health, OpenEvidence, Pulse Infoframe, and FloraWorks.

Primary Source

Neuroscience Education Institute Congress

Source Reference: Morse AM, et al "Understanding the lexicon and experience of "brain fog" in online narcolepsy and idiopathic hypersomnia communities: a social listening analysis" NEI Fall Congress 2026.

https://www.medpagetoday.com/meetingcoverage/neicongress/123777