“I use my CPAP properly every night, but the daytime sleepiness just won’t go away” — we sometimes hear this from patients who are otherwise doing everything right.
In this article, our Director walks through seven possible reasons sleepiness can persist even with consistent CPAP use.
Kazuyuki Sugaya
Director, Ueno Snoring Clinic / Anesthesiologist
Our director, with over 20,000 general anesthesia cases, focuses primarily on the diagnosis and treatment of snoring and sleep apnea, offering care tailored to each patient. [Insurance-Covered] Ueno Snoring Clinic
This article was reviewed by our Director, Kazuyuki Sugaya, and explains the possible reasons sleepiness can persist even during CPAP treatment.
Ueno Snoring Clinic takes a comprehensive approach to sleepiness, from reviewing how CPAP is being used, to assessing residual apnea, to checking for other sleep disorders that may be involved.
Insurance-Covered: Thorough Testing and Ongoing Treatment
Self-Pay: Address the Root Cause, Short-Term Focus
*If sleepiness persists, a cause other than sleep apnea may be involved, so we coordinate with other specialists as needed.
Our Director’s book, “Curing Snoring with the Latest Treatments” (ranked #1 in General Medicine and #1 in Clinical Internal Medicine, and #2 in Family Health on Amazon Japan’s bestseller charts), also covers this topic in more detail.
Quick Answer
The main reasons sleepiness can persist despite using CPAP fall into seven categories: 1) not using CPAP long enough each night, or not enough nights; 2) residual apnea, where the device’s own AHI reading hasn’t come down enough; 3) simply not getting enough total sleep time; 4) another sleep disorder occurring alongside sleep apnea; 5) psychological factors such as depression or anxiety; 6) the effects of medication, alcohol, or caffeine; and 7) lingering effects from a long period of untreated low oxygen levels. CPAP isn’t a treatment that guarantees sleepiness will disappear simply by using it — it’s important to review how it’s being used and check for causes beyond sleep apnea itself. If sleepiness continues for several weeks or more, please consult your doctor rather than trying to judge it on your own.
📋 What This Article Covers
“I use my CPAP properly every night, but the daytime sleepiness just won’t go away” — we sometimes hear this from patients who are continuing treatment. CPAP is highly effective against snoring and apnea themselves, but there are genuinely cases where sleepiness lingers even with consistent use.
This condition is medically known as “residual sleepiness,” and it’s known to occur in a subset of patients who are using CPAP correctly. There isn’t just one cause — it can range from issues with how CPAP itself is being used, to an entirely different condition hiding behind the apnea.
In this article, our Director walks through 7 possible causes of sleepiness that persists despite CPAP use, one by one.
Daytime sleepiness that persists despite consistent CPAP use is medically referred to as “residual sleepiness.” Even when the snoring and breathing disruptions from apnea have improved, sleepiness as a subjective symptom can sometimes remain — and this is seen in a certain proportion of patients.
| Cause | Category |
|---|---|
| 1. Not enough CPAP hours or nights of use | How CPAP is used |
| 2. Residual apnea (AHI hasn’t come down enough) | How CPAP is used |
| 3. Not getting enough total sleep time | Lifestyle |
| 4. Another sleep disorder occurring alongside | Coexisting condition |
| 5. Psychological factors such as depression or anxiety | Coexisting condition |
| 6. The effects of medication, alcohol, or caffeine | Lifestyle |
| 7. Lingering effects from long-term low oxygen levels | Effects of prior history |
Let’s take a closer look at each one.
To get the full benefit of CPAP, a general guideline is using it for at least 4 hours a night, ideally every night. If you’re wearing the mask but removing it partway through the night, or only managing a few nights a week, the treatment effect can end up insufficient, making residual sleepiness more likely.
That said, this doesn’t mean it’s fine to use CPAP for 4 hours and sleep the remaining hours without it. Since the goal of treatment is to minimize apnea events as much as possible, it’s important to keep the time spent sleeping without CPAP as short as you can.
Even with consistent CPAP use, mask leaks or a pressure setting that isn’t quite right can sometimes mean the device’s own recorded AHI hasn’t dropped as much as it should. In these cases, apnea itself is still occurring to some degree, which can make it harder for sleepiness to improve.
If your CPAP data shows the AHI isn’t coming down, mask leaks, mouth breathing, and weight gain are among the factors worth reviewing with your doctor. (We cover the causes of a non-improving CPAP AHI reading — mask leaks, mouth breathing, weight gain, and more — in more detail in a separate guide; please ask us about this during a consultation, as the English translation of that guide is still in progress.)
CPAP is, first and foremost, a treatment for disrupted breathing during sleep — it doesn’t increase your total amount of sleep. If your bedtime is consistently late and you’re chronically short on sleep, daytime sleepiness can persist even with CPAP working correctly. It’s worth taking a moment to reflect on your average nightly sleep duration.
There’s no single number of hours that works for everyone — the right amount of sleep varies by individual. Aim for enough sleep that you don’t feel sleepy or fatigued during the day.
Beyond sleep apnea syndrome, there are several other sleep disorders that can cause sleepiness on their own — restless legs syndrome, periodic limb movement disorder, narcolepsy, idiopathic hypersomnia, and circadian rhythm disruption from shift work, among others. When one of these coexists with sleep apnea, CPAP alone may not be enough to fully resolve the sleepiness.
Depression and anxiety are known to reduce sleep quality and can present as daytime fatigue or sleepiness. If you find that you don’t feel rested even though you’re sleeping, or you’ve had a persistent low mood, your mental state — not just sleep apnea — may also be playing a role.
A fair number of medications — antidepressants, anti-anxiety medications, antihistamines, and others — can cause drowsiness as a side effect. Alcohol before bed can lower sleep quality, and caffeine later in the day can interfere with sleep. It’s worth reviewing your current medications and daily habits as part of the picture.
When severe sleep apnea has gone untreated for many years, the repeated drops in oxygen may have an effect on the brain, and sleepiness can sometimes persist even after CPAP treatment begins. In these cases, it may simply take longer for CPAP’s benefits to become apparent compared with other causes.
Some patients, feeling that “I’ve been trying hard with CPAP but the sleepiness isn’t going away, so what’s the point,” end up stopping treatment — but we wouldn’t recommend that. The improvement in apnea itself and the improvement in sleepiness as a symptom don’t always happen on the same timeline. If your apnea has genuinely improved, that still translates into a lower risk of cardiovascular disease and other complications.
At the same time, if sleepiness continues for a long stretch, it can create real risks in daily life, such as drowsy driving. Rather than assuming “I’ll get used to it eventually,” it’s important to identify the underlying cause.
If sleepiness hasn’t improved after using CPAP consistently for a while (several weeks to a few months), we’d recommend checking on and discussing the following.
Start by reviewing your CPAP usage data — how many hours and nights you’re actually using it, and whether the device’s recorded AHI has come down sufficiently. Next, take a look at your typical sleep duration and daily rhythm, any medications you’re taking, and your alcohol or caffeine intake. If the cause still isn’t clear after that, talk with your doctor, including about the possibility of another sleep disorder or a psychological factor.
When needed, we may also coordinate with other specialists, such as psychiatry or psychosomatic medicine, to help identify the cause.
Ueno Snoring Clinic is a sleep disorder clinic specializing in snoring and sleep apnea syndrome. Beyond reviewing your CPAP usage and device data, we take a careful look at whether any factor besides apnea may be contributing to your sleepiness.
If you’re using CPAP but the sleepiness won’t go away, or you’re unsure what’s causing it, please come talk to us rather than stopping treatment on your own.
When sleepiness persists despite using CPAP, the cause could be something related to CPAP itself — insufficient usage time, or residual apnea — or it could be a range of other factors: not enough sleep overall, another sleep disorder occurring alongside, psychological factors, medication or alcohol use, or lingering effects from a past period of low oxygen levels.
Rather than simply putting up with “still sleepy despite using it” or giving up on treatment altogether, working through the possible causes one by one is the shortest path to genuinely resolving the problem.
Let’s Figure Out the Cause of Your Sleepiness Together
From reviewing how you’re using CPAP to checking for other sleep disorders that may be involved, we’re here to help every step of the way.
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From CPAP adjustments to a comprehensive evaluation of what’s behind your sleepiness, we’re happy to help. Fully appointment-based, with same-day appointments available.
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We provide medical services for international patients. Please check our English website for details on how to visit our clinic.
Supervising Physician
Kazuyuki Sugaya, Director of Ueno Snoring Clinic
After graduating from Fujita Health University School of Medicine in 2004, Dr. Sugaya began his career as an anesthesiologist at Toho University Omori Medical Center. He has since gained extensive clinical experience at municipal hospitals and private clinics nationwide, administering general anesthesia in over 20,000 cases. In 2020, he founded the "Tokyo Spine Clinic," and has served as the Director of Ueno Snoring Clinic since 2025.
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Ueno Snoring Clinic
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