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Still Tired on CPAP? When Sleep Apnoea Overlaps with Insomnia and Other Sleep Disorders

Still Tired on CPAP? When Sleep Apnoea Overlaps with Insomnia and Other Sleep Disorders

Your AHI is controlled, your usage hours are good but you still wake exhausted. Here is why that happens, which overlapping conditions to consider, and what to ask your clinical team next.


One of the most demoralising experiences in CPAP therapy is doing everything right consistent use, good mask fit, well-controlled AHI and still feeling exhausted. If this is where you are, the explanation is usually not that CPAP has stopped working. It is that something else was also contributing to your poor sleep, and CPAP, which treats one specific thing, has left that other thing untouched. Sleep medicine increasingly recognises that OSA rarely travels alone: a significant proportion of patients have two or more concurrent sleep-related conditions, each of which needs its own assessment and management.

First: Rule Out the CPAP-Specific Reasons

Before exploring overlapping sleep disorders, it is worth confirming that CPAP itself is performing as it should. Residual fatigue in a CPAP user is not automatically a sign of a second condition it can also reflect inadequate therapy delivery that needs a clinical adjustment.

✅ Check These First (CPAP-Related)

  • Is your AHI consistently below 5 on therapy?
  • Is your leak rate within target range (under ~24 L/min)?
  • Are you using CPAP for at least 7 hours most nights?
  • Is your prescribed pressure still appropriate for your current weight and anatomy?
  • Are there treatment-emergent central apnoeas in your data?
  • Is your humidifier at the right setting for the season?
  • Has your mask cushion been replaced recently?

🔍 Then Consider These (Non-CPAP Causes)

  • Do you still feel unrefreshed even on nights when data looks perfect?
  • Is it difficult to fall asleep or stay asleep despite using CPAP?
  • Do your legs feel restless, uncomfortable, or jerky at night?
  • Do you have episodes of sudden muscle weakness triggered by emotion?
  • Is your sleep schedule highly irregular or shifted (very late or very early)?
  • Do you experience vivid dream-like hallucinations as you fall asleep?
  • Has your mood been low could depression be contributing to fatigue?
🔔 If your CPAP data looks good but you remain significantly fatigued, tell your sleep clinic explicitly. "My data is controlled but I am still exhausted" is a clinically important statement that should prompt further investigation not reassurance that CPAP takes time. If your sleep clinic's response to residual fatigue with well-controlled data is simply to wait longer, it is reasonable to ask specifically what other sleep disorders might be contributing and whether further testing is warranted.
Conditions That Commonly Co-Exist With Obstructive Sleep Apnoea OSA / CPAP Insomnia (COMISA) ~30–50% of OSA PLMD / RLS Restless legs & limb movements ~26–36% of OSA Narcolepsy / IH Idiopathic hypersomnia Rare but underdiagnosed Circadian Rhythm Disorder Sleep phase shift Depression / Anxiety
Sleep disorders that commonly co-exist with OSA. Each of these can independently disrupt sleep quality or cause excessive daytime fatigue even when CPAP is successfully controlling apnoea events. OSA is rarely the only diagnosis in a significantly symptomatic patient.

COMISA: When Insomnia and Sleep Apnoea Coexist

The combination of obstructive sleep apnoea and insomnia now termed COMISA (comorbid insomnia and sleep apnoea) is increasingly recognised as one of the most clinically significant and underdiagnosed presentations in sleep medicine. Research suggests that between 30 and 50 per cent of OSA patients also have clinically significant insomnia, making it the most common overlap condition in this population.

😴
COMISA: Comorbid Insomnia and Sleep Apnoea
Affects an estimated 30–50% of OSA patients to some degree

Insomnia in the context of OSA most commonly presents as difficulty initiating or maintaining sleep lying awake for long periods despite being tired, waking frequently during the night and struggling to return to sleep, or waking earlier than intended feeling unrefreshed. The critical point is that CPAP treats the apnoea component but does nothing for the conditioned arousal, racing thoughts, and hyperarousal that maintain chronic insomnia. Many patients find that starting CPAP actually worsens their insomnia temporarily, because the mask itself becomes a conditioned arousal cue and the pressure of "having to sleep" with the device intensifies existing insomnia patterns.

Signs COMISA May Be Present
  • Difficulty falling asleep despite CPAP being on
  • Frequent waking unrelated to mask issues
  • Mind racing at bedtime or on waking at night
  • Clock-watching, frustration about sleep
  • Sleep debt despite adequate time in bed
  • Feeling worse on nights you "try harder"
First-Line Treatment
  • CBT-I (Cognitive Behavioural Therapy for Insomnia) NICE recommended first-line
  • Available via NHS Talking Therapies referral or Sleepio app (free via some NHS services)
  • Sleep restriction therapy (counterintuitive but highly effective)
  • Stimulus control to rebuild bedroom sleep association
  • NOT sleeping tablets as first-line these worsen OSA
⚠ Many sleeping tablets worsen sleep apnoea and should not be used without specialist guidance. Benzodiazepines and Z-drugs (zopiclone, zolpidem) reduce upper airway muscle tone during sleep, which directly worsens OSA severity. If you have both insomnia and sleep apnoea, standard sleeping tablets are not an appropriate first-line treatment. CBT-I (cognitive behavioural therapy for insomnia) is the evidence-based treatment that addresses insomnia without the risk of worsening your apnoea. If your GP suggests sleeping tablets for insomnia alongside CPAP, it is reasonable to ask specifically about the OSA interaction and whether CBT-I referral would be more appropriate.
👤
Periodic Limb Movement Disorder & Restless Legs Syndrome
PLMD affects an estimated 26–36% of OSA patients

Periodic Limb Movement Disorder (PLMD) involves repetitive, involuntary movements of the legs (and sometimes arms) during sleep, typically occurring every 20–40 seconds and producing brief arousals that fragment sleep without the person being aware of them. Its daytime cousin, Restless Legs Syndrome (RLS), produces uncomfortable sensations in the legs during waking rest that create an irresistible urge to move them making it difficult to sit or lie still in the evening and at bedtime.

Both conditions are independently capable of producing the same fatigue and unrefreshed waking that OSA produces, and both commonly co-occur with OSA. PLMD in particular is frequently missed because it produces no conscious awareness of its disruption a person with PLMD may genuinely believe they sleep solidly through the night while their data (or a partner's account) tells a different story.

Signs to Watch For
  • Partner reports leg kicks or jerks during sleep
  • Waking with leg cramps or aching legs
  • Uncomfortable crawling/tingling leg sensation at rest (RLS)
  • Urge to move legs relieved by movement
  • Fatigue that doesn't improve despite good CPAP data
  • High CPAP fragmentation index despite controlled AHI
Investigation & Treatment
  • In-lab polysomnography (PSG) the gold standard for PLMD diagnosis
  • Iron and ferritin blood tests (low ferritin worsens both PLMD and RLS)
  • Iron supplementation if ferritin low (discuss dose with GP)
  • Dopamine agonist medications for moderate-severe cases
  • Alpha-2-delta ligands (gabapentin/pregabalin) in some cases
  • Avoid caffeine, alcohol, antihistamines which worsen RLS
⚡
Narcolepsy and Idiopathic Hypersomnia
Rare but frequently delayed in diagnosis often by a decade or more

Narcolepsy and idiopathic hypersomnia are conditions characterised by excessive daytime sleepiness that persists regardless of how much sleep a person gets or how well their sleep is otherwise managed. Both can coexist with OSA and can be masked by it when OSA is treated and daytime sleepiness persists at levels that seem disproportionate to the CPAP data, these conditions enter the differential.

Narcolepsy type 1 is caused by the loss of hypocretin-producing neurons and has a characteristic additional symptom of cataplexy (sudden, brief muscle weakness triggered by strong emotion, particularly laughter). Narcolepsy type 2 and idiopathic hypersomnia do not have cataplexy, making them considerably harder to distinguish clinically from other causes of residual sleepiness. Both require specialist investigation that goes beyond what a standard sleep clinic can typically offer.

Characteristic Features
  • Extreme sleepiness even after adequate sleep
  • Sleep attacks — irresistible sleep onset in inappropriate situations
  • Cataplexy (narcolepsy type 1 only) muscle weakness with emotion
  • Hypnagogic hallucinations (vivid sensations on falling asleep)
  • Sleep paralysis on waking
  • Sleep inertia profound difficulty waking (IH especially)
Route to Diagnosis
  • Referral to specialist sleep centre (not standard sleep clinic)
  • MSLT (Multiple Sleep Latency Test) measures how quickly you fall asleep across 5 naps
  • PSG the night before MSLT to confirm adequate overnight sleep
  • CSF hypocretin measurement in specialist centres for narcolepsy type 1
  • Wakefulness-promoting medications if confirmed
  • Ask your sleep clinic for a specialist centre referral if suspected
🌑
Circadian Rhythm Sleep-Wake Disorders
Misalignment between the body clock and the social/work schedule

Circadian rhythm sleep-wake disorders occur when the internal body clock is shifted significantly earlier or later than the socially expected sleep window, producing chronic mismatch between when a person can sleep and when they are required to be awake. The most common form in adults is Delayed Sleep-Wake Phase Disorder (DSWPD), in which the body clock is shifted several hours later than normal making natural sleep onset very late (1–4am) and natural waking correspondingly late (9am–12pm). When work or social obligations require conventional waking times, the result is chronic sleep deprivation that CPAP cannot address because the fundamental problem is not apnoea but misaligned circadian timing.

Signs This May Be Contributing
  • Cannot fall asleep before 1–2am regardless of effort
  • Feel most alert in the late evening and night
  • Feel much better on days when you wake naturally late
  • Weekday fatigue dramatically worse than weekends
  • No difficulty sleeping — only difficulty sleeping at conventional times
  • History of this pattern since adolescence
Management Approaches
  • Timed light therapy (bright light in the morning to advance the clock)
  • Melatonin taken several hours before desired sleep onset
  • Chronotherapy (gradual schedule shifting)
  • Strict sleep schedule discipline no lie-ins
  • Referral to sleep specialist or chronobiology clinic
  • Workplace adjustments where possible (later start times)
Investigation Pathway for Residual Fatigue on CPAP STEP 1 Optimise CPAP Check AHI, leak, usage Review mask fit Review pressure setting Check for central apnoeas At sleep clinic STEP 2 Blood Tests FBC, iron, ferritin Thyroid function (TSH) Vitamin D, B12 Blood glucose / HbA1c Via GP STEP 3 Screen for Overlap Insomnia screening (ISI) RLS / PLMD symptoms Circadian history Mood / depression screen Sleep clinic + GP STEP 4 Specialist Testing In-lab PSG for PLMD MSLT for narcolepsy/IH Actigraphy for circadian CBT-I for COMISA Specialist sleep centre
A four-step investigation framework for residual fatigue on CPAP. Steps 1 and 2 can be initiated immediately via your sleep clinic and GP. Steps 3 and 4 require clinical referral and, in some cases, access to a specialist sleep centre with in-laboratory testing capability.

The Role of Mental Health and Medications

Two non-sleep-disorder causes of residual fatigue on CPAP that are frequently overlooked in clinical reviews are depression and medication side effects. Both are common, both are eminently treatable, and both can produce fatigue indistinguishable from sleep-disorder fatigue without targeted enquiry.


Depression and Fatigue: A Bidirectional Relationship
OSA and depression frequently coexist and each worsens the other

Depression is significantly more prevalent in people with OSA than in the general population, and the relationship is bidirectional: disrupted sleep worsens mood, and depression impairs sleep quality independently of apnoea. CPAP may improve mood in some patients as sleep quality improves, but it does not treat depression directly. If your fatigue is accompanied by persistent low mood, loss of interest, reduced motivation, or early morning waking with low mood, this warrants explicit assessment and treatment in its own right not simply continued optimisation of your CPAP therapy. Speak with your GP and be specific about the mood symptoms, not just the fatigue.


Medication Side Effects and Sleep
A surprisingly common and underexplored cause of residual fatigue

A wide range of commonly prescribed medications produce fatigue, poor sleep quality, or reduced sleep architecture as side effects including some antidepressants, beta-blockers, antihistamines, statins, and blood pressure medications. If you started a new medication around the same time that your fatigue worsened, or if your fatigue seems disproportionate to your otherwise well-controlled CPAP data, ask your GP to review your current medications for sleep-disruptive effects. In some cases, an equivalent medication with a different side-effect profile, or a change in timing of the dose, can make a meaningful difference without any change to your CPAP management.

How to Ask for Further Investigation: A Practical Script

Many patients with residual fatigue on CPAP leave their sleep clinic review feeling dismissed reassured that their data is good without having their symptom burden taken seriously. Knowing how to frame the conversation increases the likelihood of getting a clinical response that goes beyond data optimisation.

  • "My CPAP data shows well-controlled AHI and good usage, but I remain significantly fatigued. I would like to understand what else might be contributing." This frames residual fatigue as an unexplained clinical finding requiring investigation, not a complaint about the therapy.
  • "I have read about COMISA and PLMD as conditions that commonly overlap with OSA. Is it worth screening for these?" Naming specific conditions gives the clinician a concrete starting point and signals that you have done sufficient research to be a useful partner in the investigation.
  • "Could we arrange an Insomnia Severity Index questionnaire, and could my GP test my ferritin, thyroid function, and vitamin D levels?" Asking for specific, low-burden first steps moves the conversation from abstract discussion to concrete action.
  • "If the standard screening doesn't identify anything, would a referral to an in-laboratory sleep study or a specialist sleep centre be appropriate?" Establishing the pathway for escalation in advance means you have a clear next step if first-line investigation is unrevealing.
💡 Residual fatigue despite well-controlled CPAP is a clinical finding, not a patient problem. The appropriate clinical response to "my AHI is controlled but I am still exhausted" is investigation, not reassurance. You are not failing at CPAP, you are not being impatient, and you are not imagining the fatigue. You are describing a symptom that has not yet been fully explained, and unexplained symptoms in a treated patient deserve further diagnostic work. Holding this frame when you speak with your clinical team changes the conversation from "am I doing CPAP correctly?" to "what else do we need to find and treat?"

Frequently Asked Questions

How long should I give CPAP before concluding that residual fatigue needs further investigation?
Most sleep medicine guidelines suggest that meaningful improvement in daytime sleepiness should be apparent within four to twelve weeks of consistent, effective CPAP therapy. If your AHI is well controlled, your usage is consistent, and your fatigue has not substantially improved after three months, this is a reasonable threshold for requesting further investigation rather than continuing to wait. Some improvement in sleep quality and energy may continue gradually over a longer period, but significant, persistent fatigue at three months with well-controlled data warrants clinical attention rather than simple reassurance. Do not allow yourself to be told to "give it more time" without a specific plan for what will be investigated at what point if time alone does not resolve the symptom.
My sleep clinic says my data looks fine can I ask my GP to refer me for further sleep investigation?
Yes. Your GP can refer you independently of your sleep clinic for investigation of symptoms that your sleep clinic has not fully addressed. A referral letter citing residual excessive daytime sleepiness or unrefreshing sleep despite well-controlled CPAP therapy, with a request for specialist sleep medicine assessment, is a reasonable and appropriate GP referral. Some GP practices will also initiate blood tests for thyroid function, ferritin, vitamin B12, and vitamin D directly without requiring a specialist referral, which is a useful first step. If you feel your sleep clinic has not been responsive to your residual symptoms, framing this to your GP as an unresolved clinical concern rather than a complaint about the service tends to move toward action most efficiently.
Could it just be that I need more sleep not that I have another condition?
Yes chronic insufficient sleep (simply not spending enough time in bed) is a common and straightforward cause of ongoing fatigue that is worth ruling out before assuming a second sleep disorder. If you are using CPAP for six hours per night but your biology requires eight, CPAP will control your apnoea but will not close the sleep debt. Before pursuing complex investigation, spend two weeks prioritising eight to nine hours of time in bed with consistent sleep and wake times. If your fatigue substantially resolves, the explanation may be as simple as sleep quantity. If it does not, that result is itself useful clinical information that supports further investigation it means you are allowing adequate time for sleep and still not feeling restored, which points toward a disorder rather than a lifestyle issue.
Disclaimer: This article is intended for general informational and educational purposes only. Prevalence figures cited for comorbid conditions are approximate estimates from published research and vary by study population and diagnostic criteria. This article does not constitute medical advice. If you are experiencing persistent fatigue despite CPAP therapy, speak with your sleep clinic and GP for appropriate clinical assessment.
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