The 2001 International Classification of Sleep Disorders (ICSD) divides primary hypersomnia syndromes between narcolepsy, idiopathic hypersomnia, and the recurrent hypersomnias (like Klein-Levin syndrome); it further divides narcolepsy into that with cataplexy and that without cataplexy. This ICSD version defines narcolepsy as a disorder of unknown cause "that is characterized by excessive sleepiness that typically is associated with cataplexy and other REM-sleep phenomena, such as sleep paralysis and hypnagogic hallucinations". It also establishes baseline categorical standards for diagnosis of narcolepsy, through 2 sets of well defined criteria, as follows.

Minimal narcolepsy diagnostic criteria set #2:

- A "complaint of excessive sleepiness or sudden muscle weakness."

- Associated features that include: sleep paralysis; disrupted major sleep episode; hypnagogic hallucinations; automatic behaviors.

- Polysomnography with one or more of the following: "sleep latency less than 10 minutes;" "REM sleep latency less than 20 minutes;" an MSLT with a mean sleep latency less than 5 minutes; "two or more sleep-onset REM periods" (SOREMPs).

- "No medical or mental disorder accounts for the symptoms." (see hypersomnia differential diagnosis)

In the absence of clear cataplexy, it becomes much more difficult to make a firm diagnosis of narcolepsy. “Various terms, such as essential hypersomnia, primary hypersomnia, ambiguous narcolepsy, atypical narcolepsy, etc., have been used to classify these patients, who may be in the developing phase of narcolepsy.”

Since the 2001 ICSD, the classification of primary hypersomnias has been steadily evolving, as further research has shown more overlap between narcolepsy and idiopathic hypersomnia. The 3rd edition of the ICSD is currently being finalized, and its new classification will label narcolepsy caused by orexin deficiency as “type 1 narcolepsy,” which is almost always associated with cataplexy. The other primary hypersomnias will remain subdivided based on the presence of SOREMPs. They will be labeled: “type 2 narcolepsy,” with 2 or more SOREMPs on MSLT; and “idiopathic hypersomnia,” with less than 2 SOREMPS.

However, “there is no evidence that the pathophysiology or therapeutic response is substantially different for hypersomnia with or without SOREMPs on the MSLT.” Given this currently understood overlap of idiopathic hypersomnia and narcolepsy, the 5th edition of the Diagnostic and Statistical Manual of Mental Disorders (DSM-V) is also updating its classification of the primary hypersomnias. It reclassifies narcolepsy without cataplexy as major somnolence disorder (MSD). Additionally, MSD will encompass all syndromes of hypersomnolence not explained by low orexin concentrations, including idiopathic hypersomnia (with and without long sleep time) and long sleepers (people requiring >10 hours sleep/day).

Further complicating these updated classification schemes, overlap between narcolepsy "with" cataplexy and idiopathic hypersomnia has also been reported. A subgroup of narcoleptics with long sleep time, comprising 18% of narcoleptics in one study, had symptoms of both narcolepsy with cataplexy and idiopathic hypersomnia (long sleep time and unrefreshing naps). It is believed that this subgroup might have dysfunction in multiple arousal systems, including orexin and GABA (see idiopathic hypersomnia causes).

Diagnosis is relatively easy when all the symptoms of narcolepsy are present, but if the sleep attacks are isolated and cataplexy is mild or absent, diagnosis is more difficult. It is also possible for cataplexy to occur in isolation. Three tests that are commonly used in diagnosing narcolepsy are the polysomnogram, the multiple sleep latency test (MSLT), and administration of the Epworth Sleepiness Scale. These tests are usually performed by a sleep specialist. The polysomnogram involves continuous recording of sleep brain waves and a number of nerve and muscle functions during night time sleep. When tested, people with narcolepsy fall asleep rapidly, enter REM sleep early, and may often awaken during the night. The polysomnogram also helps to detect other possible sleep disorders that could cause daytime sleepiness.

The Epworth Sleepiness Scale is a brief questionnaire that is administered to determine the likelihood of the presence of a sleep disorder, including narcolepsy. For the multiple sleep latency test, a person is given a chance to sleep every 2 hours during normal wake times. The patient is taken in usually for an overnight sleep study. The following day the patient will have multiple tests where they will be told to nap after a full nights sleep (usually eight hours). Observations are made of the time taken to reach various stages of sleep (sleep onset latency). This test measures the degree of daytime sleepiness and also detects how soon REM sleep begins. Again, people with narcolepsy fall asleep rapidly and enter REM sleep early. Occasionally, a multiple sleep latency test can result in a false-negative for a narcoleptic.

The system which regulates sleep, arousal, and transitions between these states in humans is composed of three interconnected subsystems: the orexin projections from the lateral hypothalamus, the reticular activating system, and the ventrolateral preoptic nucleus. In narcoleptic individuals, these systems are all associated with impairments due to a greatly reduced number of hypothalamic orexin projection neurons and significantly fewer orexin neuropeptides in cerebrospinal fluid and neural tissue, compared to non-narcoleptic individuals. Those with narcolepsy generally experience the REM stage of sleep within five minutes of falling asleep, while people who do not have narcolepsy (unless they are significantly sleep deprived) do not experience REM until after a period of slow-wave sleep, which lasts for about the first hour or so of a sleep cycle.

Measuring orexin levels in a person's cerebrospinal fluid sampled in a spinal tap may help in diagnosing narcolepsy, with abnormally low levels serving as an indicator of the disorder. This test can be useful when MSLT results are inconclusive or difficult to interpret.

Idiopathic hypersomnia has historically been "difficult to diagnose at an early stage," especially because many other disorders can cause symptoms of excessive daytime sleepiness (EDS). Therefore, "at the time of presentation, most patients have had the disorder for many years."

Further complicating the diagnostic process, idiopathic hypersomnia lacks a clearly defining clinical feature. Whereas narcolepsy is associated with cataplexy and sleep-onset REM episodes, and Kleine-Levin syndrome is associated with megaphagia (compulsive food cravings) and hypersexuality, idiopathic hypersomnia has no such dramatic associated features, except perhaps sleep drunkenness. "Consequently there has been an unfortunate tendency to label all difficult-to-classify cases of excessive daytime sleepiness as idiopathic hypersomnia." For example, upper airway resistance syndrome and delayed sleep phase disorder were formerly confused with idiopathic hypersomnia, but now that they have been more clearly defined, doctors can more carefully exclude these causes of EDS in order to more correctly diagnose idiopathic hypersomnia. However, "even in the presence of other specific causes of hypersomnia, one should carefully assess the contribution of these etiological factors to the complaint of EDS and when specific treatments of these conditions fail to suppress EDS, the [additional] diagnosis of idiopathic hypersomnia should be considered."

The severity of EDS can be quantified by subjective scales, such as the Epworth sleepiness scale and the Stanford sleepiness scale (SSS), and also by objective tests, like the multiple sleep latency test (MSLT)."

In 2001, the ICSD (International Classification of Sleep Disorders) updated their criteria for the diagnosis of idiopathic hypersomnia. Essentially, EDS must be present for at least 6 months, sleep studies (polysomnography and multiple sleep latency test) must show certain characteristics, and all other known causes for long sleep time and EDS must be considered (see hypersomnia). For the patient, this diagnostic process is often tedious, expensive and time-consuming, as other than the sleep studies, it is still basically a diagnosis of exclusion.

In patients with idiopathic hypersomnia, polysomnography typically shows short sleep latency, increased mean slow wave sleep, and a high mean sleep efficiency. "Latency to REM sleep and percentages of light sleep and REM sleep were normal, compared with normal ranges." Despite this, one study has found increased sleep fragmentation in patients with idiopathic hypersomnia without long sleep time, suggesting multiple possible presentations.

It is important to note that although sleep latencies are typically short in idiopathic hypersomnia, the clinical severity may not correlate closely with the MSLT results. In fact, "latencies above 5 minutes are not uncommon in patients with clinically severe hypersomnia." When sleep latency is below 10 minutes, the presence of sleep-onset REM periods (SOREMPs) in two or more of the MSLT naps suggests a diagnosis of narcolepsy, whereas sleep periods lacking rapid eye movement (NREM sleep) in the various naps suggests a diagnosis of idiopathic hypersomnia. However, the importance of this differentiation between REM and NREM has been called into question. (see Classification)

Although the MSLT is currently the best available test to diagnose EDS in general, the MSLT protocol lacks the ability to document the extended, unrefreshing daytime naps that often occur in idiopathic hypersomnia. Complicating the matter, several groups of researchers have found normal MSLT results in patients who otherwise seem to have idiopathic hypersomnia. Therefore, when idiopathic hypersomnia is suspected, researchers suggest appending a 24-hour continuous polysomnography to the standard overnight/MSLT study in order to record total sleep time. Alternatively, an assay of the patient's cerebrospinal fluid (CSF) can be performed in order to test for an adequate level of hypocretin (to exclude narcolepsy with cataplexy) and to determine whether the patient’s CSF abnormally boosts GABA receptor sensitivity (thought to underlie many cases of idiopathic hypersomnia and narcolepsy without cataplexy). Globally, there are very few labs capable of performing the CSF assays referenced above.

It is also important to note that whereas narcolepsy is strongly associated with the HLA-DQB1*0602 genotype, "HLA typing is of no help in the positive diagnosis of idiopathic hypersomnia." This is "despite some reports that suggest an increase frequency of HLA Cw2 and DRS in idiopathic hypersomnia subjects."

The diagnosis of narcolepsy and cataplexy is usually made by symptom presentation. Presenting with the tetrad of symptoms (Excessive daytime sleepiness, sleep onset paralysis, hypnogogic hallucinations, cataplexy symptoms) is strong evidence of the diagnosis of narcolepsy. A Multiple Sleep Latency Test (MSLT) is often conducted in order to quantify daytime sleepiness.

Episodes of sleep paralysis can occur in the context of several medical conditions (e.g., narcolepsy, hypokalemia). When episodes occur independent of these conditions or substance use, it is termed "isolated sleep paralysis" (ISP). When ISP episodes are more frequent and cause clinically-significant distress and/or interference, it is classified as "recurrent isolated sleep paralysis"(RISP). Episodes of sleep paralysis, regardless of classification, are generally short (1–6 minutes), but longer episodes have been documented. With RISP the individual can also suffer back-to-back episodes of sleep paralysis in the same night, which is unlikely in individuals who suffer from ISP.

It can be difficult to differentiate between cataplexy brought on by narcolepsy and true sleep paralysis, because the two phenomena are physically indistinguishable. The best way to differentiate between the two is to note when the attacks occur most often. Narcolepsy attacks are more common when the individual is falling asleep; ISP and RISP attacks are more common upon awakening.

Several circumstances have been identified that are associated with an increased risk of sleep paralysis. These include insomnia, sleep deprivation, an erratic sleep schedule, stress, and physical fatigue. It is also believed that there may be a genetic component in the development of RISP, because there is a high concurrent incidence of sleep paralysis in monozygotic twins. Sleeping in the supine position has been found an especially prominent instigator of sleep paralysis.

Sleeping in the supine position is believed to make the sleeper more vulnerable to episodes of sleep paralysis because in this sleeping position it is possible for the soft palate to collapse and obstruct the airway. This is a possibility regardless of whether the individual has been diagnosed with sleep apnea or not. There may also be a greater rate of microarousals while sleeping in the supine position because there is a greater amount of pressure being exerted on the lungs by gravity.

While many factors can increase risk for ISP or RISP, they can be avoided with minor lifestyle changes. By maintaining a regular sleep schedule and observing good sleep hygiene, one can reduce chances of sleep paralysis. It helps subjects to reduce the intake of stimulants and stress in daily life by taking up a hobby or seeing a trained psychologist who can suggest coping mechanisms for stress. However, some cases of ISP and RISP involve a genetic factor—which means some people may find sleep paralysis unavoidable. Practicing meditation regularly might also be helpful in preventing fragmented sleep, and thus the occurrence of sleep paralysis. Research has shown that long-term meditation practitioners spend more time in slow wave sleep, and as such regular meditation practice could reduce nocturnal arousal and thus possibly sleep paralysis.

There have been some studies suggesting levothyroxine as a possible treatment for idiopathic hypersomnia, especially for patients with subclinical hypothyroidism. This treatment does carry potential risks (especially for patients without hypothyroidism or subclinical hypothroidism), which include cardiac arrhythmia.

Research is being conducted on hypocretin gene therapy and hypocretin cell transplantation for narcolepsy-cataplexy.

"The severity of daytime sleepiness needs to be quantified by subjective scales (at least the Epworth Sleepiness Scale) and objective tests such as the multiple sleep latency test (MSLT)." The Stanford sleepiness scale (SSS) is another frequently-used subjective measurement of sleepiness. After it is determined that EDS is present, a complete medical examination and full evaluation of potential disorders in the differential diagnosis (which can be tedious, expensive and time-consuming) should be undertaken.

PLMD is often treated with anti-Parkinson medication; it may also respond to anticonvulsants, benzodiazepines, and narcotics. Patients must stay on these medications in order to experience relief, because there is no known cure for this disorder.

PLMs tend to be exacerbated by tricyclic antidepressants, SSRIs, stress, and sleep deprivation. It is also advised not to consume caffeine, alcohol, or antidepressants as these substances could worsen the PLMD symptoms.

Other medications aimed at reducing or eliminating the leg jerks or the arousals can be prescribed. Non-ergot derived dopaminergic drugs (pramipexole and ropinirole) are preferred. Other dopaminergic agents such as co-careldopa, co-beneldopa, pergolide, or lisuride may also be used. These drugs decrease or eliminate both the leg jerks and the arousals. These medications are also successful for the treatment of restless legs syndrome.

In one study, co-careldopa was superior to dextropropoxyphene in decreasing the number of leg kicks and the number of arousals per hour of sleep. However, co-careldopa and, to a lesser extent, pergolide may shift the leg movements from the nighttime to the daytime.

Clonazepam (Klonopin), in doses of 1 mg has been shown to improve objective and subjective measures of sleep.

A systematic review found that traumatic childhood experiences (such as family conflict or sexual trauma) significantly increases the risk for a number of sleep disorders in adulthood, including sleep apnea, narcolepsy, and insomnia. It is currently unclear whether or not moderate alcohol consumption increases the risk of obstructive sleep apnea.

In addition, an evidence-based synopses suggests that the sleep disorder, idiopathic REM sleep behavior disorder (iRBD), may have a hereditary component to it. A total of 632 participants, half with iRBD and half without, completed self-report questionnaires. The results of the study suggest that people with iRBD are more likely to report having a first-degree relative with the same sleep disorder than people of the same age and sex that do not have the disorder. More research needs to be conducted to gain further information about the hereditary nature of sleep disorders.

A population susceptible to the development of sleep disorders is people who have experienced a traumatic brain injury (TBI). Because many researchers have focused on this issue, a systematic review was conducted to synthesize their findings. According to their results, TBI individuals are most disproportionately at risk for developing narcolepsy, obstructive sleep apnea, excessive daytime sleepiness, and insomnia. The study's complete findings can be found in the table below:

Treatments for sleep disorders generally can be grouped into four categories:

- Behavioral and psychotherapeutic treatment

- Rehabilitation and management

- Medication

- Other somatic treatment

None of these general approaches is sufficient for all patients with sleep disorders. Rather, the choice of a specific treatment depends on the patient's diagnosis, medical and psychiatric history, and preferences, as well as the expertise of the treating clinician. Often, behavioral/psychotherapeutic and pharmacological approaches are not incompatible and can effectively be combined to maximize therapeutic benefits. Management of sleep disturbances that are secondary to mental, medical, or substance abuse disorders should focus on the underlying conditions.

Medications and somatic treatments may provide the most rapid symptomatic relief from some sleep disturbances. Certain disorders like narcolepsy, are best treated with prescription drugs such as Modafinil. Others, such as chronic and primary insomnia, may be more amenable to behavioral interventions, with more durable results.

Chronic sleep disorders in childhood, which affect some 70% of children with developmental or psychological disorders, are under-reported and under-treated. Sleep-phase disruption is also common among adolescents, whose school schedules are often incompatible with their natural circadian rhythm. Effective treatment begins with careful diagnosis using sleep diaries and perhaps sleep studies. Modifications in sleep hygiene may resolve the problem, but medical treatment is often warranted.

Special equipment may be required for treatment of several disorders such as obstructive apnea, the circadian rhythm disorders and bruxism. In these cases, when severe, an acceptance of living with the disorder, however well managed, is often necessary.

Some sleep disorders have been found to compromise glucose metabolism.

It is mostly unknown what causes PLMD, but in many cases the patient also suffers from other medical problems such as Parkinson's disease or narcolepsy. Factors that increase the likelihood of PLMD in the absence of restless leg syndrome include being a shift worker, snoring, coffee drinking, stress, and use of hypnotics, particularly in the case of benzodiazepine withdrawal. For women, the presence of musculoskeletal disease, heart disease, obstructive sleep apnea, cataplexy, doing physical activities close to bedtime and the presence of a mental disorder were significantly associated with having a higher risk of both PLMD and restless legs syndrome.

Although "there has been no cure of chronic hypersomnia", there are several treatments that may improve patients' quality of life, depending on the specific cause or causes of hypersomnia that are diagnosed.

As of 1993 only approximately 30 people with AHC had been described in scientific literature. Due to the rarity and complexity of AHC, it is not unusual for the initial diagnosis to be incorrect, or for diagnosis to be delayed for several months after the initial symptoms become apparent. The average age of diagnosis is just over 36 months. Diagnosis of AHC is not only difficult because of its rarity, but because there is no diagnostic test, making this a diagnosis of exclusion. There are several generally accepted criteria which define this disorder, however other conditions with a similar presentation, such as HSV encephalitis, must first be ruled out. Due to these diagnostic difficulties, it is possible that the commonness of the disease is underestimated.

The following descriptions are commonly used in the diagnosis of AHC. The initial four criteria for classifying AHC were that it begins before 18 months of age, includes attacks of both hemiplegia on either side of the body, as well as other autonomic problems such as involuntary eye movement (episodic monocular nystagmus), improper eye alignment, choreoathetosis, and sustained muscle contractions (dystonia). Finally, patients suffer from intellectual disabilities, delayed development, and other neurological abnormalities. These diagnostic criteria were updated in 1993 to include the fact that all of these symptoms dissipate immediately upon sleeping. Diagnostic criteria were also expanded to include episodes of bilateral hemiplegia which shifted from one side of the body to the other.

Recent criteria have been proposed for screening for AHC early, in order to improve the diagnostic timeline. These screening criteria include focal or unilateral paroxysmal dystonia in the first 6 months of life, as well as the possibility of flaccid hemiplegia either with or separate from these symptoms. Paroxysmal ocular movements should also be considered, and these should include both binocular and monocular symptoms which show in the first 3 months of life.

A wide array of phenomena may resemble epileptic seizures, which may lead to people who do not have epilepsy being misdiagnosed. Indeed, a significant percentage of people initially diagnosed with epilepsy will later have this revised. In one study, the majority of children referred to a secondary clinic with "fits, faints and funny turns" did not have epilepsy, with syncope (fainting) as the most common alternative. In another study, 39% of children referred to a tertiary epilepsy centre did not have epilepsy, with staring episodes in mentally challenged children as the most common alternative. In adults, the figures are similar, with one study reporting a 26% rate of misdiagnosis.

Differentiation of a non-epileptic attack from an epileptic seizure includes the patient keeping their eyes closed and rarely causing themselves harm (both more common in non-epileptic attacks)

Overall outcomes for AHC are generally poor, which is contributed to by AHC's various diagnostic and management challenges. In the long term, AHC is debilitating due to both the hemiplegic attacks and permanent damage associated with AHC. This damage can include cognitive impairment, behavioral and psychiatric disorders, and various motor impairments. There is, however, not yet any conclusive evidence that AHC is fatal or that it shortens life expectancy, but the relatively recent discovery of the disorder makes large data for this type of information unavailable. Treatment for AHC has not been extremely successful, and there is no cure. There are several drugs available for treatment, as well as management strategies for preventing and dealing with hemiplegic attacks.

Non-epileptic seizures are paroxysmal events that mimic an epileptic seizure but do not involve abnormal, rhythmic discharges of cortical neurons. They are caused by either physiological or psychological conditions. The latter is discussed more fully in psychogenic non-epileptic seizures.

[Please could somebody add an actual description of what happens when somebody has a seizure or 'paroxysmal event'?!]

Favorable response to treatment with the ADHD drug methylphenidate (Ritalin) has been reported, but this treatment option is not acceptable to all patient families.

Dr. Lane Robson, of The Children’s Clinic in Calgary, Alberta, says "If a child is having a wetting episode once a month, medicating them daily is probably not a good treatment. If it’s a daily issue, you may have to make that decision."

Treatment of any kind of complex visual hallucination requires an understanding of the different pathologies in order to correctly diagnose and treat. If a person is taking a pro-hallucinogenic medication, the first step is to stop taking it. Sometimes improvement will occur spontaneously and pharmacotherapy is not necessary. While there is not a lot of evidence of effective pharmacological treatment, antipsychotics and anticonvulsants have been used in some cases to control hallucinations. Since peduncular hallucinosis occurs due to an excess of serotonin, modern antipsychotics are used to block both dopamine and serotonin receptors, preventing the overstimulation of the lateral geniculate nucleus. The drug generically called carbamazepine increases GABA, which prevents the LGN from firing, thereby increasing the inhibition of the LGN. Regular antipsychotics as well as antidepressants can also be helpful in reducing or eliminating peduncular hallucinosis.

More invasive treatments include corrective surgery such as cataract surgery, laser photocoagulation of the retina, and use of optical correcting devices. Tumor removal can also help to relieve compression in the brain, which can decrease or eliminate peduncular hallucinosis. Some hallucinations may be due to underlying cardiovascular disease, so in these cases the appropriate treatment includes control of hypertension and diabetes. As described, the type of treatment varies widely depending on the causation behind the complex visual hallucinations.

Episodes of giggle incontinence are embarrassing and socially incapacitating, diminishing the quality of life. Those having the condition learn to adapt by avoiding activities that may bring on laughter. Other approaches include limiting fluid intake, trying to remain seated, and concealing leakage by wearing absorbent pads and dark clothing.

Other visual hallucinations tend to stem from psychological disorders. Whereas a person with a psychological disorder thinks their hallucinations are real, people with peduncular hallucinosis normally know that the visual hallucinations they see are not real. Peduncular hallucinations are independent of seizures, unlike some other visual hallucinations.

The affective spectrum is a spectrum of affective disorders (mood disorders). It is a grouping of related psychiatric and medical disorders which may accompany bipolar, unipolar, and schizoaffective disorders at statistically higher rates than would normally be expected. These disorders are identified by a common positive response to the same types of pharmacologic treatments. They also aggregate strongly in families and may therefore share common heritable underlying physiologic anomalies.

Affective spectrum disorders include:

- Attention deficit hyperactivity disorder

- Bipolar disorder

- Body dysmorphic disorder

- Bulimia nervosa and other eating disorders

- Cataplexy

- Dysthymia

- Generalized anxiety disorder

- Hypersexuality

- Irritable bowel syndrome

- Impulse-control disorders

- Kleptomania

- Migraine

- Major depressive disorder

- Obsessive-compulsive disorder

- Oppositional defiant disorder

- Panic disorder

- Posttraumatic stress disorder

- Premenstrual dysphoric disorder

- Social anxiety disorder

- Fibromyalgia

The following may also be part of the spectrum accompanying affective disorders.

- Chronic pain

- Intermittent explosive disorder

- Pathological gambling

- Personality disorder

- Pyromania

- Substance abuse and addiction (includes alcoholism)

- Trichotillomania

Also, there are now studies linking heart disease.

Many of the terms above overlap. The American Psychiatric Association's definitions of these terms can be found in the "Diagnostic and Statistical Manual of Mental Disorders" (DSM).

The lifespan of patients with NPC is usually related to the age of onset. Children with antenatal or infantile onset usually succumb in the first few months or years of life, whereas adolescent and adult onset forms of Niemann–Pick type C have a more insidious onset and slower progression, and affected individuals may survive to the seventh decade. Adult cases of NPC are being recognized with increasing frequency. It is suspected that many patients affected by NPC are undiagnosed, owing to lack of awareness of the disease and the absence of readily available screening or diagnostic tests. For the same reasons the diagnosis is often delayed by many years.

Niemann–Pick type C is diagnosed by assaying cultured fibroblasts for cholesterol esterfication and staining for unesterified cholesterol with filipin. The fibroblasts are grown from a small skin biopsy taken from a patient with suspected NPC. The diagnosis can be confirmed by identifying mutations in the NPC1 or NPC2 genes in 80–90% of cases. This specialized testing is available at Thomas Jefferson University Lysosomal Disease Testing Lab and the Mayo Clinic.