Written and medically reviewed by Kwaku Osafo-Mensah, MD
Pulmonary Medicine | Sleep Medicine | Diplomate, American Board of Sleep Medicine (ABSM)
Medically reviewed: August 2026
Sleep apnea does not always occur evenly throughout the night.
For some people, obstructive breathing events become substantially more frequent—or more physiologically significant—during rapid eye movement (REM) sleep.
A sleep-study report may therefore show a relatively modest overall apnea-hypopnea index (AHI) but a much higher REM AHI.
Such findings can be confusing.
Does a high REM AHI mean you have severe sleep apnea? Can sleep apnea be important if the overall AHI is only mild? And what happens if your sleep study captured very little REM sleep?
REM AHI can provide important information, but it must be interpreted together with the overall study, oxygenation, symptoms, body position, amount of REM sleep recorded, and the clinical situation.
What Is REM Sleep?
REM stands for rapid eye movement sleep.
Normal sleep cycles between non-REM and REM sleep several times during the night.
REM sleep is characterized by distinctive brain activity, rapid eye movements, vivid dreaming, and a substantial reduction in skeletal-muscle tone.
This reduction in muscle activity is normal and helps prevent us from physically acting out most dreams.
But changes in upper-airway muscle activity during REM can also make the airway more susceptible to obstruction in people predisposed to obstructive sleep apnea.
Why Can Sleep Apnea Become Worse During REM?
The upper airway depends partly on neuromuscular activity to remain open during sleep.
During REM sleep, changes in upper-airway muscle tone and respiratory control can increase airway collapsibility in susceptible individuals.
As a result, obstructive events during REM may sometimes be
- More frequent
- Longer
- Associated with deeper oxygen desaturation
- More concentrated during particular portions of the night
This is one reason an overall nightly AHI may not completely describe an individual’s pattern of sleep-disordered breathing.
What Is REM AHI?
REM AHI is the average number of scored apneas and hypopneas that occur per hour of REM sleep.
Conceptually:
REM AHI = apneas + hypopneas occurring during REM ÷ hours of REM sleep
A sleep report may, therefore, provide several respiratory indices, such as
- Overall AHI
- REM AHI
- Non-REM AHI
- Supine AHI
- Non-supine AHI
Each provides a different view of when respiratory events occurred.
For a detailed explanation of the basic AHI measurement, see AHI Explained: What Your Apnea-Hypopnea Index Means.
How Can Overall AHI Be Mild While REM AHI Is High?
Consider a simplified example.
Suppose someone sleeps for six hours:
- Five hours of non-REM sleep
- One hour of REM sleep
Relatively few events occur during non-REM sleep, but 35 apneas and hypopneas occur during the one hour of REM sleep.
The person’s
REM AHI could be 35 events/hour
while the overall AHI may still fall into a substantially lower category because REM represents only one portion of the total night’s sleep.
This illustrates an important principle:
A nightly average can dilute a concentrated period of more severe obstruction.
That does not mean the overall AHI should be ignored. It means the stage-specific information may provide additional clinical context.
Does a High REM AHI Mean Severe Sleep Apnea?
Not automatically.
Adult OSA severity classifications are generally based on the overall respiratory-event index used for the diagnostic study, interpreted within the clinical context.
A high REM AHI tells us that obstruction was more frequent during REM sleep.
It does not automatically convert a mild overall AHI into a diagnosis of severe OSA.
However, a high REM AHI may still be clinically relevant, particularly when considered alongside:
- Symptoms
- Daytime sleepiness
- Oxygen desaturation
- Duration of respiratory events
- Cardiovascular or metabolic conditions
- Amount of REM sleep captured
- Body position
- Study methodology
- Other relevant clinical factors
The correct interpretation therefore goes beyond assigning another severity label.
How Much REM Sleep Was Recorded?
This is one of the most important questions when interpreting REM AHI.
A stage-specific index becomes less stable when the patient spends very little time in that stage.
For example, suppose only 10 minutes of REM sleep are recorded.
A relatively small number of respiratory events during those 10 minutes can produce a mathematically high REM AHI.
That number may be meaningful, but it should be interpreted cautiously because the denominator is small.
When reviewing REM-related findings, ask:
- How many minutes of REM sleep were recorded?
- Was the amount of REM representative of a usual night?
- Did REM occur in more than one sleep cycle?
- Were the respiratory events consistently concentrated during REM?
- What happened to oxygen saturation during those events?
The REM AHI should always be interpreted together with the amount of REM sleep used to calculate it.
Why a Sleep Study May Capture Too Little REM Sleep
Many factors can influence the amount of REM sleep recorded during a study.
These may include:
- Short total sleep time
- Frequent awakenings
- First-night laboratory effects
- Medications
- Alcohol
- Sleep deprivation or unusual sleep timing
- Medical conditions
- Certain psychiatric conditions
- Early termination of the study
- Individual night-to-night variation
REM sleep also tends to become more prominent during the latter portion of the sleep period.
A study that ends unusually early may therefore capture less REM sleep than a typical full night.
Why Oxygen Desaturation May Be Worse During REM
In some people, obstructive respiratory events during REM sleep are associated with greater oxygen desaturation.
Several factors may contribute, including:
- Longer respiratory events
- Changes in ventilation during REM
- Reduced respiratory-muscle contribution
- Lower baseline oxygen reserve in people with pulmonary disease
- More severe upper-airway obstruction
This finding means two people with the same REM AHI may still experience different physiologic consequences.
The depth and duration of oxygen desaturation matter in addition to the event count.
For more information, see Sleep Apnea and Oxygen Levels: How Low Is Too Low?
REM Sleep Apnea and Body Position
REM sleep and body position can interact.
For example, respiratory events may be particularly prominent when someone is
in REM sleep + sleeping on the back
A report might, therefore, show differences among:
- REM AHI
- Non-REM AHI
- Supine AHI
- Non-supine AHI
But interpreting these combinations requires enough sleep in the relevant conditions.
If someone spends only a few minutes both supine and in REM sleep, the calculated rate may be based on a minimal denominator.
REM and body position can interact, particularly when obstructive events cluster during supine REM sleep. For a deeper explanation, see Positional Sleep Apnea: Why Sleeping on Your Back Can Make OSA Worse.
This is another reason the raw index should not be interpreted without examining how much time contributed to it.
Can You Have Sleep Apnea Only During REM?
Some people demonstrate respiratory events that are strongly concentrated during REM sleep, with relatively few events during non-REM sleep.
Terms such as REM-related OSA, REM-predominant OSA, and REM-isolated OSA appear in the medical literature.
However, definitions have varied across studies.
There is not one universally applied numerical definition that should be imposed on every report.
When describing REM-related disease, it is, therefore, useful to consider the following:
- Overall AHI
- REM AHI
- Non-REM AHI
- Ratio of REM to non-REM events
- Amount of REM sleep recorded
- Symptoms
- Oxygenation
- Body position
- Clinical context
Who Is More Likely to Have REM-Predominant OSA?
Research has found REM-predominant patterns in different patient groups, and some studies have reported associations with factors such as female sex and less severe overall OSA.
However, REM-related obstruction can occur across a broad range of patients.
Individual diagnosis should not be based on demographic patterns alone.
The sleep study itself and the clinical context remain more important.
Does REM Sleep Apnea Cause Symptoms?
It can, but symptoms do not correlate perfectly with stage-specific AHI.
Potential symptoms of obstructive sleep apnea include:
- Daytime sleepiness
- Fatigue
- Nonrestorative sleep
- Morning headaches
- Impaired concentration
- Mood changes
- Snoring
- Witnessed breathing pauses
- Gasping or choking during sleep
Some people with REM-predominant OSA may have significant symptoms, while others may report relatively little daytime impairment.
The absence of obvious sleepiness does not by itself prove that the respiratory findings are irrelevant.
Does REM Sleep Apnea Affect Cardiovascular Health?
Research has examined relationships between REM-related obstructive sleep apnea and cardiovascular or metabolic outcomes.
Some observational studies have suggested associations between REM-related OSA and conditions such as hypertension.
However, these relationships are complex.
An association does not automatically prove that treating every elevated REM AHI will prevent a specific cardiovascular outcome.
Clinical decisions should therefore integrate the entire patient’s risk profile rather than relying on broad claims based on one stage-specific index.
Can a Home Sleep Apnea Test Measure REM AHI?
Many conventional home sleep apnea tests do not record the EEG, eye movements, and chin muscle activity used to determine sleep stages during laboratory polysomnography.
Therefore, they generally cannot provide the same directly measured REM AHI as a standard in-lab polysomnogram.
Some newer home technologies use additional physiologic signals or algorithms that may estimate sleep stages or related states, but capabilities vary substantially by device.
When REM-related disease is an important clinical question, the methodology of the test matters.
For a detailed comparison, see Home Sleep Apnea Test vs. Lab Sleep Study: Which One Do You Need?
Can a Home Test Underestimate REM-Related Sleep Apnea?
Potentially.
A home study may underestimate respiratory-event frequency for several reasons, including use of monitoring time rather than EEG-confirmed sleep time in many conventional systems.
In addition, if the device does not measure sleep stages, it may fail to show that respiratory events are concentrated specifically during REM sleep.
A negative or apparently mild home test therefore needs to be interpreted in the context of symptoms, study quality, and clinical suspicion.
Does REM-Related Sleep Apnea Need Treatment?
There is no single treatment rule based solely on REM AHI.
Management decisions may consider:
- Overall AHI or REI
- REM AHI
- Non-REM AHI
- Symptoms
- Daytime sleepiness
- Oxygenation
- Relevant medical conditions
- Driving or occupational risk
- Body position
- Patient preferences
- Treatment tolerance
- Diagnostic-study quality
A patient with a mild overall AHI but substantial REM-related obstruction, clinically important symptoms, or significant oxygen abnormalities may warrant a different discussion than someone with similar numbers but few symptoms and limited physiologic disturbance.
For more about individualized decisions in lower-range OSA, see Mild Sleep Apnea: Does It Need Treatment?
PAP Therapy and REM Sleep
Positive airway pressure can prevent upper-airway collapse throughout different sleep stages when it is used effectively.
But there is an important practical issue:
REM sleep often becomes more prominent later in the sleep period.
A person who uses CPAP for only the first few hours of the night and then removes it may leave a substantial portion of later REM sleep untreated.
This is one reason PAP adherence should not be thought of only as reaching a minimum number of hours.
Ideally, PAP should be used throughout the entire sleep period, including naps when appropriate.
Learn more in CPAP & PAP Therapy.
What If My CPAP AHI Is Low but I Remove the Mask Early?
A low machine-reported residual AHI while PAP is being worn can indicate effective control during the treated period.
But the machine generally cannot tell you what happened after the mask was removed.
If PAP is removed before later-night REM-rich sleep, untreated obstructive events may occur after therapy stops.
This is why both treatment effectiveness and treatment duration matter.
Does Positional Therapy Treat REM Sleep Apnea?
Sometimes positional factors contribute, but REM-related and positional OSA are not the same thing.
If obstruction occurs mainly during REM regardless of body position, simply avoiding back sleeping may inadequately control the disorder.
If events are concentrated during supine REM, positional therapy may have greater relevance.
The sleep study should be examined carefully before assuming that position alone explains the pattern.
Can Weight Loss Improve REM-Related OSA?
Weight reduction can improve obstructive sleep apnea severity in many people with overweight or obesity, but responses vary.
Weight management may be an important component of treatment when appropriate, but it should not automatically be assumed to eliminate clinically meaningful REM-related obstruction.
Follow-up assessment may be necessary when substantial weight change occurs.
What Should You Look for in Your Sleep Study?
If your report mentions REM-related sleep apnea, useful questions include:
- What was my overall AHI score?
- What was my REM AHI?
- What was my non-REM AHI?
- How many minutes of REM sleep were recorded?
- Was the REM AHI based on enough REM sleep to interpret confidently?
- Was apnea worse while sleeping on my back?
- What happened to my oxygen saturation during REM?
- Were the REM events longer or associated with deeper desaturation?
- Was this a laboratory study or a home sleep apnea test?
- How do my symptoms and medical conditions affect interpretation?
- Does the REM pattern change the treatment discussion?
- If I use PAP, am I wearing it through the entire sleep period?
REM AHI Should Not Be Read in Isolation
REM AHI can reveal clinically useful information that the overall nightly average may obscure.
But it is still only one component of the sleep study.
A thoughtful interpretation considers the following:
Overall AHI + REM AHI + non-REM AHI + amount of REM sleep + oxygenation + body position + symptoms + medical history + study quality.
This is the same principle that applies to AHI more generally:
One number rarely tells the entire story.
The Bottom Line
REM-related obstructive sleep apnea occurs when breathing abnormalities substantially concentrate or worsen during REM sleep.
A high REM AHI can be important, but it should not automatically be interpreted as equivalent to the overall severity classification of the entire night.
The amount of REM sleep recorded, oxygen desaturation, body position, symptoms, medical conditions, and study methodology all matter.
The most useful question is not simply
“How high was my REM AHI?”
The more useful question is
“How much REM sleep was measured, what happened to my breathing and oxygen during REM, and how should those findings affect my overall treatment plan?”
That is the more clinically meaningful interpretation.
References & Further Reading
- Mokhlesi B, Finn LA, Hagen EW, et al. Obstructive sleep apnea during REM sleep and hypertension: results of the Wisconsin Sleep Cohort. American Journal of Respiratory and Critical Care Medicine. 2014;190(10):1158–1167.
https://doi.org/10.1164/rccm.201406-1136OC - Varga AW, Mokhlesi B. REM obstructive sleep apnea: risk for adverse health outcomes and novel treatments. Sleep and Breathing. 2019;23(2):413–423.
https://doi.org/10.1007/s11325-018-1727-2 - Kapur VK, Auckley DH, Chowdhuri S, et al. Clinical practice guideline for diagnostic testing for adult obstructive sleep apnea. Journal of Clinical Sleep Medicine. 2017;13(3):479–504.
https://doi.org/10.5664/jcsm.6506 - Patil SP, Ayappa IA, Caples SM, et al. Treatment of adult obstructive sleep apnea with positive airway pressure: an American Academy of Sleep Medicine clinical practice guideline. Journal of Clinical Sleep Medicine. 2019;15(2):335–343.
https://doi.org/10.5664/jcsm.7640 - Berry RB, Quan SF, Abreu AR, et al. The AASM Manual for the Scoring of Sleep and Associated Events: Rules, Terminology, and Technical Specifications. American Academy of Sleep Medicine.
Medical Author & Reviewer
Kwaku Osafo-Mensah, MD
Pulmonary Medicine | Sleep Medicine
Diplomate, American Board of Sleep Medicine (ABSM)
More than 20 years of experience in sleep medicineMedically reviewed: August 2026
About the medical reviewer · Editorial Policy
Medical Disclaimer: This information is provided for general educational purposes and is not a substitute for individualized medical evaluation, diagnosis, or treatment. Discuss sleep-study findings, symptoms, PAP therapy, and treatment decisions with a qualified healthcare professional.