Sleep in [ME/CFS] shows marked night-to-night fluctuation under free-living conditions—results from a matched case-control study, 2026, Saurel+

[SNT Gatchaman]

Sleep in myalgic encephalomyelitis/chronic fatigue syndrome shows marked night-to-night fluctuation under free-living conditions—results from a matched case-control study

Spoiler: Authors

Saurel, Maïtena; Fornasieri, Isabelle; Del Sordo, Giovanna C; Chatain, Cyril; Fantini, Maria Livia; Gruet, Mathieu; Saidi, Oussama

PURPOSE
Unrefreshing and non-restorative sleep is a hallmark complaint in people with myalgic encephalomyelitis/chronic fatigue syndrome (ME/CFS). However, little is known about their habitual sleep and night-to-night fluctuations under real-life conditions. This study aimed to characterize sleep, and the intraindividual variability (IIV) of sleep in people living with ME/CFS compared with matched controls.

METHODS
In this case-control study, 38 ME/CFS and 38 controls wore a wrist accelerometer continuously for 7 days and completed concurrent sleep diaries, the Pittsburgh Sleep Quality Index (PSQI), and Epworth Sleepiness Scale (ESS). Within the ME/CFS group, participants were also stratified by symptom severity using the Bell Disability Scale. Sleep IIV was quantified using the coefficient of variation, the root mean square of successive differences, and the Bayesian variability model, respectively.

RESULTS
Compared with controls, individuals with ME/CFS spent significantly more time in bed and exhibited poorer sleep efficiency (SE) (all p < 0.05). Despite a longer time in bed, total sleep time did not differ between groups. ME/CFS participants also displayed significantly greater IIV in SE. By contrast, sleep timing (bedtime) was more regular among ME/CFS. Exploratory analyses did not detect clear differences across ME/CFS severity subgroups for mean sleep variables or variability indices.

CONCLUSION
Under real-life conditions, people with ME/CFS exhibit poor sleep quality and unstable SE. These findings highlight sleep IIV as a clinically relevant dimension of sleep health in ME/CFS. Brief summary Current knowledge/study rationale Unrefreshing sleep is a core symptom of ME/CFS, yet most evidence relies on single- or two-night laboratory assessments that may not reflect habitual sleep under real-life conditions. Moreover, night-to-night sleep variability, a potentially critical dimension of sleep health, has not been systematically examined in ME/CFS. Study impact Using week-long wrist accelerometry, this study shows that under free-living conditions sleep in ME/CFS is characterized not only by impaired sleep efficiency but also by pronounced night-to-night variability, despite relatively stable bedtime compared to controls. These findings highlight sleep efficiency variability as a clinically relevant feature of ME/CFS and underscore the need for multi-night assessment and targeted strategies addressing sleep variability.

BRIEF SUMMARY
Current knowledge/study rationale
Unrefreshing sleep is a core symptom of ME/CFS, yet most evidence relies on single- or two-night laboratory assessments that may not reflect habitual sleep under real-life conditions. Moreover, night-to-night sleep variability, a potentially critical dimension of sleep health, has not been systematically examined in ME/CFS.

Study impact
Using week-long wrist accelerometry, this study shows that under free-living conditions sleep in ME/CFS is characterized not only by impaired sleep efficiency but also by pronounced night-to-night variability, despite relatively stable bedtime compared to controls. These findings highlight sleep efficiency variability as a clinically relevant feature of ME/CFS and underscore the need for multi-night assessment and targeted strategies addressing sleep variability.

Web | DOI | PDF | Journal of Clinical Sleep Medicine | Open Access

 

[Amw66]

It would be interesting to see if all sleep phases were collated - my daughter has very little deep sleep - both fitbit and Garmin were vey similar for this.

 

[ryanc97]

There was discussion before on this drug Xyrem here or on PR. Apparently some person took it and it didn’t nothing.

Makes your sleep more deep or something.

 

[Hoopoe]

Do the marked night-tonight fluctuations correlate with overexertion on that day and PEM or worse symptoms on the next day?

I also experience fluctuations in sleep quality that don't seem to be dependent on exertion, but overexertion seems to be a trigger for poor sleep, which is then typically followed by a day with worse symptoms and less ability to function.

 

[Hoopoe]

Sleep normally exhibits some degree of night-to-night fluctuation in response to environmental, psychosocial, and physiological influences [28]. However, the magnitude of variability observed in ME/CFS exceeded that reported in healthy populations and was comparable to levels documented in clinical sleep disorders such as insomnia

 

[Mij]

Do the marked night-tonight fluctuations correlate with overexertion on that day and PEM or worse symptoms on the next day?

Not for me. Poor sleep, insomnia and PEM are not related in my exprience.

 

[Yann04]

participants were also stratified by symptom severity using the Bell Disability Scale.

That‘s not measuring symptom severity but severity of disability. Useful to stratify and they are no doubt correlated but the authors should not conflate the two.

By contrast, sleep timing (bedtime) was more regular among ME/CFS.

And yet most of the advice we seem to get for sleep is „sleep hygiene“. Our sleep hygiene is literally better than healthy people according to this statistic.

Brief summary Current knowledge/study rationale Unrefreshing sleep is a core symptom of ME/CFS, yet most evidence relies on single- or two-night laboratory assessments that may not reflect habitual sleep under real-life conditions. Moreover, night-to-night sleep variability, a potentially critical dimension of sleep health, has not been systematically examined in ME/CFS. Study impact Using week-long wrist accelerometry, this study shows that under free-living conditions sleep in ME/CFS is characterized not only by impaired sleep efficiency but also by pronounced night-to-night variability, despite relatively stable bedtime compared to controls. These findings highlight sleep efficiency variability as a clinically relevant feature of ME/CFS and underscore the need for multi-night assessment and targeted strategies addressing sleep variability.

BRIEF SUMMARY
Current knowledge/study rationale
Unrefreshing sleep is a core symptom of ME/CFS, yet most evidence relies on single- or two-night laboratory assessments that may not reflect habitual sleep under real-life conditions. Moreover, night-to-night sleep variability, a potentially critical dimension of sleep health, has not been systematically examined in ME/CFS.

Study impact
Using week-long wrist accelerometry, this study shows that under free-living conditions sleep in ME/CFS is characterized not only by impaired sleep efficiency but also by pronounced night-to-night variability, despite relatively stable bedtime compared to controls. These findings highlight sleep efficiency variability as a clinically relevant feature of ME/CFS and underscore the need for multi-night assessment and targeted strategies addressing sleep variability.

I think you have a formatting error repeating the same thing twice under the conclusion header.

 

[Andy]

Do the marked night-tonight fluctuations correlate with overexertion on that day and PEM or worse symptoms on the next day?

When I've done too much I always experience worse sleep.

 

[Yann04]

When I've done too much I always experience worse sleep.

Same. It‘s more restless and thus often shorter. My heart is beating faster I‘m more likely to have night sweats etc.

 

[forestglip]

This seems very much worth exploring to me, just based on my own experience, and now seeing this paper. One of the most striking things about my sleep is how much the time asleep changes night to night. It seems to be mainly tied to over-exertion causing less sleep the following night. And it's not just that I fall asleep later. After high-exertion days, I sometimes wake up very early even though I would love to sleep in.

This is the past three months for my time asleep. It seems to me to be a lot of bouncing between low and high sleep duration.


(Note: This isn't objectively measured. When I wake up, I calculate the difference between when I woke up and about 15 minutes after turning off my phone the night before, or my best guess for when I fell asleep if that metric isn't helpful on a given night.)

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The thread study study looked at three models, and it seems that increased variability was seen with coefficient of variation (CV) and root mean square of successive differences (RMSSD), but not with the Bayesian Variability Model (BVM).

I don't know too much about these models, but the discussion about it seems to say that this may suggest that the sleep variability seen in ME/CFS is due to external factors such as how much exertion people do, which would align with my experience.

Conventional dispersion indices (CV and RMSSD) consistently indicated greater night-to-night fluctuations in estimated SE and related parameters in ME/CFS. In contrast, the Bayesian variability model, which isolates stable latent variability while accounting for measurement uncertainty, did not reveal corresponding group differences.

This divergence may suggest that the observed variability may primarily reflect context-dependent fluctuations rather than a fixed, trait-like increase in underlying variability.

Importantly, the residual component captured by CV and RMSSD may in fact encode physiologically meaningful responses to daily perturbations. In ME/CFS, such perturbations could include variations in symptom burden, physical or cognitive exertion, and post-exertional malaise (PEM).

The finding of reduced bedtime variability alongside unstable SE further supports this interpretation, suggesting that individuals with ME/CFS may actively maintain regular sleep schedules as an adaptive pacing strategy, yet remain unable to achieve consistent sleep continuity due to fluctuating internal constraints.

We therefore propose that pronounced night-to-night sleep variability in ME/CFS may partly reflect the characteristic “push-and-crash” dynamic of the illness.

Edit: Fixed typo.

 

[Rick Sanchez]

When I've done too much I always experience worse sleep.

Yes, if I have slightly overdone it, worse sleep is in fact often the first symptom. This was especially the case when I was mild.

 

[Felis Catus]

I also experience fluctuations in sleep quality that don't seem to be dependent on exertion, but overexertion seems to be a trigger for poor sleep, which is then typically followed by a day with worse symptoms and less ability to function.

Me, too.

And another one which I find quite annoying is that if I have a particularly good night's sleep and sleep 30-60 mins longer than usual, then I struggle to fall asleep the next night and have poor sleep.

 

[ryanc97]

I used to have fragmented sleep, waking up every few hours but IVIG fixed that for some reason.

 

[Mij]

Returning to work after recovering from PVFS decades ago gradually and negatively affected my sleep, I ended up feeling like a freight train was racing through my head. I could not shut my brain off or sleep. I ended up with severe insomnia and retired from working.

My normal sleep returned 2 weeks later, but I relapsed.