Although central and obstructive sleep apnea have some signs and symptoms in common, others are present in one but absent in another, enabling differential diagnosis as between the two types:

Signs and symptoms of sleep apnea generally

- Signs:

- Symptoms:

Signs and symptoms of central sleep apnea

- Signs:

- Symptoms:

Signs and symptoms of and conditions associated with obstructive sleep apnea

- Signs:

- Symptoms:

- Associated conditions:

Common symptoms of OSA include unexplained daytime sleepiness, restless sleep, and loud snoring (with periods of silence followed by gasps). Less common symptoms are morning headaches; insomnia; trouble concentrating; mood changes such as irritability, anxiety and depression; forgetfulness; increased heart rate and/or blood pressure; decreased sex drive; unexplained weight gain; increased urination and/or nocturia; frequent heartburn or gastroesophageal reflux disease; and heavy night sweats.

A diagnosis of sleep apnea requires determination by a physician. The examination may require a study of an individual in a sleep lab, although the AAST has said a two belt IHT (In Home Test) will replace a PSG for diagnosing obstructive apnea. There, the patient will be monitored while at rest, and the periods when breathing ceases will be measured with respect to length and frequency. During a PSG (polysomnography) (a sleep study), a person with sleep apnea shows breathing interruptions followed by drops/reductions in blood oxygen and increases in blood carbon dioxide level.

- In adults, a pause must last 10 seconds to be scored as an apnea. However, in young children, who normally breathe at a much faster rate than adults, shorter pauses may still be considered apneas.

- Hypopneas in adults are defined as a 30% reduction in air flow for more than ten seconds, followed by oxygen-saturation declines of at least 3% or 4% per the AASM stndards. and/or EEG arousal. The Apnea-Hypopnea Index (AHI) is expressed as the number of apneas or hypopneas per hour of sleep.

As noted above, in central sleep apnea, the cessation of airflow is associated with the absence of physical attempts to breathe; specifically, polysomnograms reveal correlation between absence of rib cage and abdominal movements and cessation of airflow at the nose and lips. By contrast, in obstructive sleep apnea, pauses are not correlated with the absence of attempts to breathe and may even be correlated with more effortful breathing in an instinctive attempt to overcome the pressure on the sufferer's airway. If the majority of a sleep-apnea sufferer's apneas/hypopneas are central, his condition is classified as central; likewise, if the majority are obstructive, his condition is classified as obstructive.

The hallmark symptom of OSA syndrome in adults is excessive daytime sleepiness. Typically, an adult or adolescent with severe long-standing OSA will fall asleep for very brief periods in the course of usual daytime activities if given any opportunity to sit or rest. This behavior may be quite dramatic, sometimes occurring during conversations with others at social gatherings.

The hypoxia (absence of oxygen supply) related to OSA may cause changes in the neurons of the hippocampus and the right frontal cortex. Research using neuro-imaging revealed evidence of hippocampal atrophy in people suffering from OSA. They found that in more than 25% of the OSA cases, this problem results in irreversible problems in mentally manipulating non-verbal information and in executive functions and working memory, despite years of optimal continuous positive airway pressure (CPAP) treatment.

Diagnosis of obstructive sleep apnea is significantly more common among people in relationships, who are alerted to their condition by being informed by their sleeping partner since individuals with obstructive sleep apnea are often unaware of the condition. There is a stigma associated with loud snoring, and it is not considered a feminine trait. Consequently, females are less likely to be told by their partners that they snore, or to admit it to themselves or doctors. Furthermore, CPAP is also perceived negatively by females, and less likely to be utilized to its full extent in this group.

Obstructive sleep apnea (OSA) is the most common category of sleep-disordered breathing. The muscle tone of the body ordinarily relaxes during sleep, and at the level of the throat the human airway is composed of collapsible walls of soft tissue which can obstruct breathing. Mild occasional sleep apnea, such as many people experience during an upper respiratory infection, may not be significant, but chronic severe obstructive sleep apnea requires treatment to prevent low blood oxygen (hypoxemia), sleep deprivation, and other complications.

Individuals with low muscle tone and soft tissue around the airway (e.g., because of obesity) and structural features that give rise to a narrowed airway are at high risk for obstructive sleep apnea. The elderly are more likely to have OSA than young people. Men are more likely to suffer sleep apnea than women and children are, though it is not uncommon in the last two population groups.

The risk of OSA rises with increasing body weight, active smoking and age. In addition, patients with diabetes or "borderline" diabetes have up to three times the risk of having OSA.

Common symptoms include loud snoring, restless sleep, and sleepiness during the daytime. Diagnostic tests include home oximetry or polysomnography in a sleep clinic.

Some treatments involve lifestyle changes, such as avoiding alcohol or muscle relaxants, losing weight, and quitting smoking. Many people benefit from sleeping at a 30-degree elevation of the upper body or higher, as if in a recliner. Doing so helps prevent the gravitational collapse of the airway. Lateral positions (sleeping on a side), as opposed to supine positions (sleeping on the back), are also recommended as a treatment for sleep apnea, largely because the gravitational component is smaller in the lateral position. Some people benefit from various kinds of oral appliances such as the Mandibular advancement splint to keep the airway open during sleep. Continuous positive airway pressure (CPAP) is the most effective treatment for severe obstructive sleep apnea but oral appliances are considered a first line approach equal to CPAP for mild to moderate sleep apnea according to the AASM parameters of care. There are also surgical procedures to remove and tighten tissue and widen the airway.

Snoring is a common finding in people with this syndrome. Snoring is the turbulent sound of air moving through the back of the mouth, nose, and throat. Although not everyone who snores is experiencing difficulty breathing, snoring in combination with other risk factors has been found to be highly predictive of OSA. The loudness of the snoring is not indicative of the severity of obstruction, however. If the upper airways are tremendously obstructed, there may not be enough air movement to make much sound. Even the loudest snoring does not mean that an individual has sleep apnea syndrome. The sign that is most suggestive of sleep apneas occurs when snoring "stops".

Other indicators include (but are not limited to): hypersomnolence, obesity BMI >30, large neck circumference ( in women, in men), enlarged tonsils and large tongue volume, micrognathia, morning headaches, irritability/mood-swings/depression, learning and/or memory difficulties, and sexual dysfunction.

The term "sleep-disordered breathing" is commonly used in the U.S. to describe the full range of breathing problems during sleep in which not enough air reaches the lungs (hypopnea and apnea). Sleep-disordered breathing is associated with an increased risk of cardiovascular disease, stroke, high blood pressure, arrhythmias, diabetes, and sleep deprived driving accidents. When high blood pressure is caused by OSA, it is distinctive in that, unlike most cases of high blood pressure (so-called essential hypertension), the readings do "not" drop significantly when the individual is sleeping. Stroke is associated with obstructive sleep apnea.

It has been revealed that people with OSA show tissue loss in brain regions that help store memory, thus linking OSA with memory loss. Using magnetic resonance imaging (MRI), the scientists discovered that people with sleep apnea have mammillary bodies that are about 20 percent smaller, particularly on the left side. One of the key investigators hypothesized that repeated drops in oxygen lead to the brain injury.

Some people with sleep apnea have a combination of both types; its prevalence ranges from 0.56% to 18%. The condition is generally detected when obstructive sleep apnea is treated with CPAP and central sleep apnea emerges. The exact mechanism of the loss of central respiratory drive during sleep in OSA is unknown but is most likely related to incorrect settings of the CPAP treatment and other medical conditions the person has.

The word "hypopnea" uses combining forms of "" + "", from the Greek roots "hypo-" (meaning "low", "under", "beneath", "down", "below normal") and "pnoia" (meaning "breathing"). See pronunciation information at "dyspnea".

The most common hypopnea symptom is excessive sleepiness, which results from constant sleep interruption. People with hypopnea due to airflow obstruction often have loud, heavy snoring that is interrupted with choking sounds or loud snorts followed by periods of silence, because not enough air can flow into the lungs through the mouth and nose. The periods of silence can last 20 seconds or longer and can happen many times each hour, resulting in poor sleep and reduced levels of oxygen in the blood.

Other symptoms of hypopnea may include depression, forgetfulness, mood or behavior changes, trouble concentrating, loss of energy, nervousness, and morning headaches. Not all people with hypopnea experience all of these symptoms and not everyone who has these symptoms has hypopnea.

Catathrenia is a rapid eye movement sleep parasomnia consisting of end-inspiratory apnea (breath holding) and expiratory groaning during sleep. Catathrenia is distinct from both somniloquy and obstructive sleep apnea. The sound is produced during exhalation as opposed to snoring which occurs during inhalation. It is usually not noticed by the person producing the sound but can be extremely disturbing to sleep partners. Bed partners generally report hearing the person take a deep breath, hold it, then slowly exhale; often with a high-pitched squeak or groaning sound.

Catathrenia typically, sometimes even exclusively, occurs during REM sleep, although it may also occur to a lesser degree during NREM sleep. Catathrenia begins with a deep inspiration. The sufferer holds her or his breath against a closed glottis, similar to the Valsalva maneuver. After a period of time and some blood oxygen desaturation, there is an arousal, followed by expiration. Expiration can be slow and accompanied by sound caused by vibration of the vocal cords or a simple rapid exhalation with no sound.

There is debate about whether the cause is physical or neurological, a question that requires further study. While some speculate about a direct correlation to high anxiety and stress or the concept that catathrenia is purely psychological, there is only anecdotal evidence of either proposed cause.

Catathrenia has been defined as a parasomnia in the International Classification of Sleep Disorders Diagnostic and Coding Manual (ICSD-2), but there is debate about its classification.

There are a few other similaritiesamongst catathrenia sufferers that have not yet been studied properly:

- Many catathrenia sufferers mention that they also suffer from some form of stress or anxiety in their lives.

- Sufferers themselves do not feel like they are experiencing a sleep apnea; the breath-holding appears to be controlled though the unconscious. Oxygen desaturation during a catathrenia episode is usually negligible.

- Many took part in sports activities during teens and twenties some which required breath-holding which included many types of sports such as swimming and even weight lifting. They find a certain level of comfort in breath-holding, and often do it while awake.

- Observations have been made of instances of breath holding during daily activities that require concentration.

- Some sufferers recalled suffering from lucid or stress dreams during their catathrenia episodes during their sleep.

- Some sufferers complain of having a painful chest upon waking from sleep.

Because catathrenia itself is not considered life-threatening, there has been very little research done in the medical community, and many experts assume that the way to treat catathrenia is to treat the underlying sleep apnea, though there is no conclusive evidence published that catathrenia results from sleep apnea, and sleep studies show that not all sufferers of catathrenia have been diagnosed with sleep apnea.

While doctors tend to dismiss it as an inconvenience, sufferers routinely describe the condition's highly negative effects on their daily lives including tiredness, low energy, dizziness and vertigo, work problems, relationship and social issues, and other physical and mental problems that could be associated with low sleep quality.

Symptoms of UARS are similar to those of obstructive sleep apnea, but are usually less severe. Fatigue, daytime sleepiness, unrefreshing sleep, and frequent awakenings during sleep are the most common symptoms.

Many patients experience chronic insomnia that creates both a difficulty falling asleep and staying asleep. As a result, patients typically experience frequent sleep disruptions. Loud snoring also serves as a possible indicator of the syndrome, but is not a symptom required for diagnosis.

Some patients experience hypotension, which may cause lightheadedness, and patients with UARS are also more likely to experience headaches and irritable bowel syndrome.

Upper airway resistance syndrome is caused when the upper airway narrows without closing. Consequently, airflow is either reduced or compensated for through an increase in inspiratory efforts. This increased activity in inspiratory muscles leads to the arousals during sleep which patients may or may not be aware of.

A typical UARS patient is not obese and possesses a triangular face and misaligned jaw, which can result in a smaller amount of space behind the base of the tongue. Patients may have other anatomical abnormalities that can cause UARS such as deviated septum or nasal valve collapse. UARS affects equal numbers of males and females. It is unclear as to whether UARS is merely a phase that occurs between simple snoring and sleep apneas, or whether UARS is a syndrome that describes a deviation from normal upper airway physiology.

Children with UARS may experience symptoms due to minor anomalies of the facial bones or due to enlarged tonsils or adenoids.

Recurrent Isolated Sleep Paralysis is an inability to perform voluntary movements at sleep onset, or upon waking from sleep.

Mixed apnea is a combination of both central and obstructive factors. The majority of premature infants with sleep apnea have mixed apnea.

Catathrenia, a rapid-eye-movement sleep parasomnia consisting of breath holding and expiratory groaning during sleep, is distinct from both somniloquy and obstructive sleep apnea. The sound is produced during exhalation as opposed to snoring which occurs during inhalation. It is usually not noticed by the person producing the sound but can be extremely disturbing to sleep partners, although once aware of it, sufferers tend to be woken up by their own groaning as well. Bed partners generally report hearing the person take a deep breath, hold it, then slowly exhale; often with a high-pitched squeak or groaning sound.

Obstructive apnea occurs when the airway passages are obstructed and little to no air exchange occurs, resulting in impaired breathing. In some cases, it occurs when patients are born with a small airway opening. Patients with obstructive apnea often have vigorous inspiratory effort but the efforts are still ineffective. Normally, the muscles at the level of the throat relax and dilate while asleep in order to open up airway however, patients with obstructive apnea may have decreased neuromuscular tone of the muscles responsible for dilating the pharynx during sleep. The inability of the vocal cords to move and the presence of a foreign body may also cause obstructive apnea. Cases of obstructive apnea are rarely found in infants that are healthy.

Nocturnal awakenings are more common in older patients and have been associated with depressive disorders, chronic pain, obstructive sleep apnea, obesity, alcohol consumption, hypertension, gastroesophageal reflux disease, heart disease, menopause, prostate problems, and bipolar disorders.

Nocturnal awakenings can be mistaken as shift work disorder.

There are over 30 recognized kinds of dyssomnias. Major groups of dyssomnias include:

- Intrinsic sleep disorders – 12 disorders recognized, including

- idiopathic hypersomnia,

- narcolepsy,

- periodic limb movement disorder,

- restless legs syndrome,

- sleep apnea,

- sleep state misperception.

- Extrinsic sleep disorders – 13 disorders recognized, including

- alcohol-dependent sleep disorder,

- food allergy insomnia,

- inadequate sleep routine.

- Circadian rhythm sleep disorders, both intrinsic and extrinsic – 6 disorders recognized, including

- advanced sleep phase syndrome,

- delayed sleep phase syndrome,

- jetlag,

- shift work sleep disorder.

A sleep diary should be kept to aid in diagnosis and for chronicling the sleep schedule during treatment. Other ways to monitor the sleep schedule are actigraphy or use of a Continuous Positive Airway Pressure (CPAP) machine that can log sleeping times

The following are possible warning signs:

- sleeping off and on in a series of naps during the day and at night, with no regular pattern but with normal total sleep time,

- difficulty getting restorative sleep, and

- excessive daytime sleepiness.

Because of the changes in sleep/wake time, and because this is a rare disorder, initially it can seem like another circadian rhythm sleep disorder such as non-24-hour sleep–wake disorder or like insomnia.

Dyssomnias are a broad classification of sleeping disorders involving difficulty getting to sleep, remaining asleep, or of excessive sleepiness.

Dyssomnias are primary disorders of initiating or maintaining sleep or of excessive sleepiness and are characterized by a disturbance in the amount, quality, or timing of sleep.

Patients may complain of difficulty getting to sleep or staying asleep, intermittent wakefulness during the night, early morning awakening, or combinations of any of these. Transient episodes are usually of little significance. Stress, caffeine, physical discomfort, daytime napping, and early bedtimes are common factors.

The universal feature of night terrors is inconsolability, very similar to that of a panic attack. During night terror bouts, people are usually described as "bolting upright" with their eyes wide open and a look of fear and panic on their faces. They will often scream. Furthermore, they will usually sweat, exhibit rapid breathing, and have a rapid heart rate (autonomic signs). In some cases, individuals are likely to have even more elaborate motor activity, such as a thrashing of limbs—which may include punching, swinging, or fleeing motions. There is a sense that the individuals are trying to protect themselves and/or escape from a possible threat of bodily injury. Although people may seem to be awake during a night terror, they will appear confused, be inconsolable and/or unresponsive to attempts to communicate with them, and may not recognize others familiar to them. Occasionally, when a person with a night terror is awakened, they will lash out at the one awakening them, which can be dangerous to that individual. Most people who experience this do not remember the incident the next day. Sleepwalking is also common during night terror bouts, as sleepwalking and night terrors are different manifestations of the same parasomnia.

During lab tests, subjects are known to have very high voltages of electroencephalography (EEG) delta activity, an increase in muscle tone, and a doubled increase in heart rate, if not more. Brain activities during a typical episode show theta and alpha activity when using an EEG. It is also common to see abrupt arousal from NREM sleep that does not progress into a full episode of a night terror. These episodes can include tachycardia. Night terrors are also associated with intense autonomic discharge of tachypnea, flushing, diaphoresis, and mydriasis – that is, unconscious or involuntary rapid breathing, reddening of the skin, profuse sweating, and dilation of the pupils.

In children with night terrors, there is no increased occurrence of psychiatric diagnoses. However, in adults who suffer from night terrors there is a close association with psychopathology or mental disorders. There may be an increased occurrence of night terrors—particularly among those suffering or having suffered from post-traumatic stress disorder (PTSD) and generalized anxiety disorder (GAD). It is also likely that some personality disorders may occur in individuals with night terrors, such as dependent, schizoid, and borderline personality disorders. There have been some symptoms of depression and anxiety that have increased in individuals that have suffered from frequent night terrors. Low blood sugar is associated with both pediatric and adult night terrors. A study of adults with thalamic lesions of the brain and brainstem have been occasionally associated with night terrors. Night terrors are closely linked to sleepwalking and frontal lobe epilepsy.

The true primary hypersomnias include these: narcolepsy (with and without cataplexy); idiopathic hypersomnia; and recurrent hypersomnias (like Klein-Levin syndrome).

ISWD has various causes, including neurological disorders such as dementia (particularly Alzheimer's Disease), brain damage, or mental retardation. It is thought that sufferers have a weak circadian clock. The risk for the disorder increases with age, but only due to increased prevalence of co-morbid medical disorders.

Hypersomnia can be primary (of central/brain origin), or it can be secondary to any of numerous medical conditions. More than one type of hypersomnia can coexist in a single patient. Even in the presence of a known cause of hypersomnia, the contribution of this cause to the complaint of EDS needs to be assessed. When specific treatments of the known condition do not fully suppress EDS, additional causes of hypersomnia should be sought. For example, if a patient with sleep apnea is treated with CPAP (continuous positive airway pressure) which resolves their apneas but not their EDS, it is necessary to seek other causes for the EDS. Obstructive sleep apnea “occurs frequently in narcolepsy and may delay the diagnosis of narcolepsy by several years and interfere with its proper management.”

RBD is characterized by the dreamer acting out his or her dreams. These dreams often involve kicking, screaming, punching, grabbing, and even jumping out of bed. When awakened, people can usually recall the dream they were having, which will match the actions they were performing, but they will not be aware that they were moving. In a normal sleep cycle, REM sleep may be experienced at intervals of between 90 minutes and two hours every night, which means RBD episodes may occur up to four times a night. In a rare case, they may only happen once a week or once a month. Episodes occur more towards the morning hours because that is when REM sleep is more frequent. The actions in an episode can result in injuries to oneself or one's bed partner. People can also respond to other people while sleeping and not even know it. This causes them to be aware of things while they are sleeping, which can result in sleep deprivation.

Excessive daytime sleepiness (EDS) is characterized by persistent sleepiness and often a general lack of energy, even during the day after apparently adequate or even prolonged nighttime sleep. EDS can be considered as a broad condition encompassing several sleep disorders where increased sleep is a symptom, or as a symptom of another underlying disorder like narcolepsy, sleep apnea or a circadian rhythm sleep disorder.

Some persons with EDS, including those with hypersomnias like narcolepsy and idiopathic hypersomnia, are compelled to nap repeatedly during the day; fighting off increasingly strong urges to sleep during inappropriate times such as while driving, while at work, during a meal, or in conversations. As the compulsion to sleep intensifies, the ability to complete tasks sharply diminishes, often mimicking the appearance of intoxication. During occasional unique and/or stimulating circumstances, a person with EDS can sometimes remain animated, awake and alert, for brief or extended periods of time. EDS can affect the ability to function in family, social, occupational, or other settings. A proper diagnosis of the underlying cause and ultimately treatment of symptoms and/or the underlying cause can help mitigate such complications.