Written and medically reviewed by Kwaku Osafo-Mensah, MD
Pulmonary Medicine | Sleep Medicine | Diplomate, ABSM
Medically reviewed: August 2026
Sleep apnea is a common sleep-related breathing disorder in which breathing repeatedly decreases or stops during sleep. These interruptions can fragment sleep, reduce oxygen levels, and place additional stress on the cardiovascular and nervous systems.
Many people have sleep apnea for years without realizing it. Loud snoring may be the first clue, but sleep apnea can also occur without prominent snoring.
This guide explains the major types of sleep apnea, common symptoms, how sleep apnea is diagnosed, and the treatment options available.
What Is Sleep Apnea?
Sleep apnea occurs when normal breathing is repeatedly interrupted during sleep. These events may result from obstruction of the upper airway, reduced respiratory drive from the brain, or a combination of both.
The three major categories are the following:
Obstructive Sleep Apnea (OSA)
Obstructive sleep apnea is the most common form. During sleep, muscles supporting the upper airway relax. In susceptible individuals, the airway becomes narrowed or temporarily collapses despite continued respiratory effort.
Central Sleep Apnea (CSA)
Central sleep apnea occurs when respiratory effort temporarily decreases or stops because the brain’s respiratory control system does not send an appropriate signal to breathe.
Central apnea may occur in association with certain medical conditions, medications, high altitude, or abnormalities of respiratory control.
Central and obstructive apneas may both cause pauses in breathing, but respiratory effort distinguishes the two patterns. Learn more in Central vs. Obstructive Sleep Apnea: What’s the Difference?
Mixed or Complex Sleep Apnea
Some people experience both obstructive and central respiratory events. Central events can also emerge in certain patients after PAP therapy is initiated for obstructive sleep apnea.
Common Symptoms of Sleep Apnea
Symptoms can vary considerably. Common clues include:
- Loud or habitual snoring
- Witnessed pauses in breathing during sleep
- Gasping, choking, or snorting during sleep
- Frequent nighttime awakenings
- Morning headaches
- Dry mouth upon awakening
- Excessive daytime sleepiness
- Fatigue or reduced energy
- Difficulty concentrating
- Memory problems
- Irritability or mood changes
- Frequent nighttime urination
Not everyone with sleep apnea experiences all of these symptoms.
Who Is at Risk?
Risk factors for obstructive sleep apnea include excess body weight, certain craniofacial or upper-airway anatomy, increasing age, family history, nasal obstruction, and use of alcohol or sedating medications.
Sleep apnea can occur in men and women of any body size, including individuals who are not overweight.
How Is Sleep Apnea Diagnosed?
Diagnosis generally requires objective sleep testing.
Two commonly used approaches are as follows:
Home Sleep Apnea Testing
A home test for sleep apnea, often abbreviated HSAT, measures selected physiologic signals while you sleep at home. It can be appropriate for certain adults with a high clinical suspicion for uncomplicated obstructive sleep apnea.
In-Laboratory Polysomnography
Polysomnography is a comprehensive overnight sleep study performed in a sleep laboratory. It measures sleep stages along with breathing, oxygen levels, heart rhythm, body movements, and other physiologic signals.
It remains particularly useful when the diagnosis is uncertain or when other sleep, respiratory, neurologic, or cardiac disorders may be present.
Choosing between home and laboratory testing depends on the clinical situation. A home study can be highly useful in appropriately selected patients, while polysomnography provides more comprehensive physiologic information when the diagnosis is uncertain or the clinical situation is more complex.
See Home Sleep Apnea Test vs. Lab Sleep Study: Which One Do You Need?
Understanding AHI
One number commonly reported on a sleep study is the Apnea-Hypopnea Index (AHI).
During polysomnography, AHI represents the average number of apneas and hypopneas occurring per hour of measured sleep.
In adults, AHI is commonly categorized approximately as follows:
- Less than 5: generally below the diagnostic threshold for adult OSA
- 5–14.9: mild sleep apnea
- 15–29.9: moderate sleep apnea
- 30 or greater: severe sleep apnea
AHI is important, but it is not the entire clinical picture. Symptoms, oxygen desaturation, event duration, sleep architecture, cardiovascular conditions, and other findings can also influence clinical decision-making.
For a more detailed explanation of AHI severity ranges, REM and positional AHI, oxygen levels, RDI, and the limitations of AHI, see our guide: AHI Explained: What Your Apnea-Hypopnea Index Means.
Understanding Your Sleep Apnea Pattern
A single overall AHI does not always describe how obstructive sleep apnea behaves throughout the night.
Sleep apnea can vary according to sleep stage, body position, oxygen response, and the type of sleep study performed. Two people with the same overall AHI may therefore have quite different sleep-study findings and treatment considerations.
AHI, RDI, and REI
Sleep-study reports may use different respiratory indices depending on the type of study and the measurements available.
AHI, RDI, and REI are related, but they are not always interchangeable.
Learn more in AHI vs RDI vs REI: What’s the Difference on a Sleep Study?
The type of respiratory event also matters. Obstructive and central apneas differ primarily in whether respiratory effort continues during the event. See Central vs. Obstructive Sleep Apnea: What’s the Difference?
Oxygen Levels
The lowest oxygen saturation is important, but it should not be interpreted in isolation.
Baseline oxygen, depth and duration of desaturation, oxygen desaturation index (ODI), time spent below specified oxygen thresholds, respiratory-event patterns, and underlying cardiopulmonary disease all affect how we interpret the lowest oxygen saturation.
Learn more in Sleep Apnea and Oxygen Levels: How Low Is Too Low?
REM-Related Sleep Apnea
Obstructive sleep apnea may become substantially worse during REM sleep.
A relatively modest overall AHI can sometimes coexist with a much higher REM AHI. The amount of REM sleep recorded, oxygenation, body position, and symptoms all matter when interpreting this pattern.
Learn more in REM-Related Sleep Apnea: What Does REM AHI Mean?
Positional Sleep Apnea
Some people experience substantially more upper-airway obstruction while sleeping on their back.
The supine AHI, non-supine AHI, amount of sleep recorded in each position, REM sleep, and treatment response help determine whether positional therapy is useful.
Learn more in Positional Sleep Apnea: Why Sleeping on Your Back Can Make OSA Worse.
Home vs. Laboratory Sleep Testing
A home sleep apnea test and an in-lab polysomnogram are not simply the same test performed in different locations.
They measure different amounts of physiologic information and are appropriate in different clinical situations.
Learn more in Home Sleep Apnea Test vs. Lab Sleep Study: Which One Do You Need?
When central sleep apnea is suspected, respiratory-effort signals and the overall breathing pattern can be particularly important. See Central vs. Obstructive Sleep Apnea: What’s the Difference?
How Is Sleep Apnea Treated?
Treatment depends on the type and severity of sleep apnea as well as symptoms, anatomy, medical conditions, and patient preferences. For a side-by-side guide to the major treatment approaches—and how factors such as OSA severity, oxygenation, sleeping position, REM sleep, body weight, anatomy, PAP tolerance, and patient preference influence the choice—see Sleep Apnea Treatment Options: CPAP, Oral Appliances, Weight Loss, Inspire, Surgery, and More.
Options may include:
PAP Therapy
Positive airway pressure therapy—including CPAP, APAP, and in selected circumstances bilevel PAP—is one of the most effective treatments for obstructive sleep apnea.
Oral Appliance Therapy
Certain patients with obstructive sleep apnea may benefit from a professionally fitted mandibular advancement device. For a detailed explanation of how mandibular advancement devices work, who may be a candidate, effectiveness compared with CPAP, side effects, titration, and follow-up testing, see Oral Appliance Therapy for Sleep Apnea: How It Works, Who Qualifies, and Does It Work?
Weight Management
When excess body weight contributes to airway obstruction, weight reduction can improve obstructive sleep apnea and overall cardiometabolic health. For a detailed discussion of how obesity affects OSA and how lifestyle weight loss, GLP-1–based medications, tirzepatide, and bariatric surgery may affect sleep apnea, see Sleep Apnea and Obesity: Can Weight Loss, GLP-1 Drugs, or Bariatric Surgery Improve OSA?
Positional Therapy
Some people experience substantially more obstruction while sleeping on their back. Positional therapy may be useful in selected cases. For a detailed guide to positional treatment—including who may benefit, side sleeping, positional devices, vibrotactile therapy, head-of-bed elevation, effectiveness, adherence, combination therapy, and follow-up testing—see Positional Therapy for Sleep Apnea: Does Sleeping on Your Side Really Work?
Surgery and Other Therapies
Selected patients may benefit from upper-airway surgery, hypoglossal nerve stimulation, or other interventions after appropriate specialist evaluation. For a detailed explanation of hypoglossal nerve stimulation—including how Inspire works, candidacy, DISE, effectiveness, implantation, programming, risks, and long-term follow-up—see Inspire for Sleep Apnea: How Hypoglossal Nerve Stimulation Works, Who Qualifies, and Does It Work?
For a comprehensive guide to anatomic sleep apnea surgery—including tonsillectomy, UPPP and other palatal procedures, tongue-base surgery, maxillomandibular advancement (MMA), nasal surgery, multilevel surgery, success rates, risks, recovery, and postoperative testing—see Sleep Apnea Surgery: Types, Who Qualifies, Success Rates, Risks, and Alternatives.
Why Treat Sleep Apnea?
Untreated sleep apnea may contribute to impaired daytime alertness and quality of life and is associated with several important health conditions.
These include hypertension and cardiovascular, metabolic, and cerebrovascular disease. The relationship between sleep apnea and these conditions is complex, and individual risk varies.
Effective treatment can improve symptoms and sleep-related quality of life and may provide additional health benefits depending on the individual.
A mild AHI does not automatically mean treatment is unnecessary. See Mild Sleep Apnea: Does It Need Treatment?
Where Should You Start?
If you are concerned about sleep apnea, the next step is usually an appropriate clinical evaluation rather than purchasing equipment on your own.
The Sleep Breathing Guide will help you understand the following:
Sleep Tests — HSAT, polysomnography, AHI, RDI, oxygen measurements, and sleep-study reports.
CPAP & PAP Therapy — CPAP, APAP, bilevel therapy, masks, humidification, comfort, and troubleshooting.
Better Sleep — evidence-based guidance on sleep habits, insomnia, circadian health, snoring, exercise, sleep environment, and improving sleep quality.
Reviews & Comparisons — evidence-informed guides to equipment and products used in sleep and breathing care.
References & Further Reading
- American Academy of Sleep Medicine (AASM). International Classification of Sleep Disorders, Third Edition, Text Revision (ICSD-3-TR). American Academy of Sleep Medicine; 2023.
- 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 - Gottlieb DJ, Punjabi NM. Diagnosis and management of obstructive sleep apnea: a review. JAMA. 2020;323(14):1389–1400.
https://doi.org/10.1001/jama.2020.3514 - American Academy of Sleep Medicine. Sleep Education — Obstructive Sleep Apnea.
https://sleepeducation.org/sleep-disorders/obstructive-sleep-apnea/
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 symptoms and treatment decisions with a qualified healthcare professional.