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SLEEP DISORDERS: Definition, Causes, Symptoms and Types

What is sleep?

Sleep is an innate, periodic and biological rhythm that provides rest to the body and mind of an individual. It occurs when our eyes close and consciousness is partially or completely lost. It results in a decrease in body movement and response to external stimulus.


What is a sleep disorder?

Sleep disorders or sleep-wake disorders are characterized by a difficulty with the quality, timing and amount of sleep. The problems often result in daytime distress and overall impairment in functioning. Sleep disorders often commonly occur with other medical and psychological conditions like depression, anxiety or cognitive disorders.


What are the causes of sleep disorders?

Various factors can play a role in the imbalance of the sleep-wake cycle, some of them are-

  • Physical conditions– Disturbances occurring in the body like chronic pain due to arthritis, persistent headaches, fibromyalgia, inflammatory bowel disease may prevent the individual in sustaining their sleep.
  • Medical illnesses– Kidney diseases, asthma, hyperthyroidism are found to affect the sleep patterns of patients.
  • Psychological disorders– Some common disorders like depression, anxiety, panic attacks, bipolar disorder is a common cause of sleep disorders, mainly insomnia.
  • Stress– Stress can be caused by mundane activities or some significant events in an individual’s life which can thereby disturb the sleep cycle.
  • Medications– Various drugs like anti-depressants, blood pressure medication, some cold medicines have been found to interfere with sleep.
  • Genetics– Research has found a genetic cause for narcolepsy, which is a neurological disorder of sleep regulation that has an effect on control of sleep and wakefulness.
  • Aging– it has been seen that more than half of adults over the age of 65 suffer from some kind of sleep disorder.
  • Environmental issues– A bright light, loud noise, uncomfortable bed, snoring partner can often be challenging and may lead to significant distress while sleeping.


What are the symptoms of sleep disorders?

Symptoms of sleep disorders vary depending on the severity and type of disorder. They may be different in case of other existing conditions. Some of the common symptoms are-

  • Difficulty falling or maintaining sleep
  • Daytime fatigue
  • Irregular breathing patterns
  • Strong urge to take daytime naps
  • Unusual or unpleasant tendencies to move while falling asleep
  • Unusual experiences while asleep
  • Irritability or anxiety
  • Depression
  • Irregular patterns of sleep-wake cycle
  • Impaired performance at work or school
  • Lack of concentration
  • Weight gain


What are the types of sleep disorders?

Some of the sleep disorders are-

1. Insomnia 

Insomnia can be described as a difficulty in initiating or maintaining sleep throughout. It is characterized by multiple awakenings during the sleeping period and problem in returning to sleep after awakening. There are also symptoms of early morning awakenings characterized by inability to return to sleep.

The insomnia can be-

  • Episodic: Symptoms last for a minimum of month but less than 3 months.
  • Persistent: Symptoms last for 3 months or longer than three months.
  • Recurrent: Two (or more) episodes within the period of 1 year.


Research indicates that approximately one-third of adults report symptoms of insomnia, 10%-15% experience associated daytime impairments, and 6% -10% have symptoms that meet the criteria for insomnia disorder. Insomnia is the most common among sleep-wake disorders.

2. Hypersomnolence Disorder

This disorder is characterized by self-reported excessive sleepiness, after the minimum sleep period of 7-8 hours. The individual has a recurrent urge to sleep multiple times within a single day. The prolonged sleep period is not freshening and there is a difficulty being completely awake after abrupt awakening.

Categories based on the duration of the symptoms-

  • Acute: Symptoms last less than 1 month.
  • Subacute: Symptoms occur for a minimum of 1 month and less than three months.
  • Persistent: Symptoms last for more than 3 months.

Categories based on severity of the symptoms-

  • Mild: Difficulty maintaining daytime alertness 1-2 days per week.
  • Moderate: Difficulty maintaining daytime alertness 3-4 days in a week.
  • Severe: Difficulty maintaining daytime alertness 5-7 days per week.


Approximately 5%-10% of individuals facing difficulties with daytime sleepiness are diagnosed of having hypersomnolence disorder. This disorder is found to occur equally among men and women.

3. Narcolepsy 

Narcolepsy is a chronic sleep disorder characterized by frequent periods of an irrepressible urge to sleep, lapsing into sleep, or napping within the same day

Individuals with narcolepsy may suffer from-

Episodes of cataplexy–  Cataplexy is characterized by sudden bilateral loss of muscle tone which causes physical changes, slurred speech and weakness in the muscles. The episodes may last up to several minutes. In some individuals, these episodes occur once or twice in year whereas some experience them daily.

Changes in rapid eye movement (REM) sleep- Most dreams are experienced during the REM stage of sleep. REM sleep stage is reached at any time of the day in people with narcolepsy. People suffering from narcolepsy transition quickly to REM sleep, usually within 15 minutes of falling asleep.

Excessive daytime sleepiness– individuals suffering from narcolepsy fall asleep without warning, anywhere, anytime.

Hypocretin deficiency

Categories based on severity-

  • Mild: Inconsistent episodes of cataplexy (less than once per week), need for naps only once or twice in a day, and mildly disturbed night-time sleep.
  • Moderate: Cataplexy occurs once daily or every few days, disturbed nocturnal sleep, and need for frequent naps daily.
  • Severe: Drug-resistant cataplexy with multiple attacks daily, nearly constant sleepiness, and disturbed nocturnal sleep including body movements, insomnia, and vivid dreaming


In most countries, narcolepsy-cataplexy affects 0.02%-0.04% of the population. Both genders are affected by narcolepsy but males show higher dominance.

4. Obstructive Sleep Apnea-Hypopnea

Apnea is referred to the total absence of airflow

Hypopnea refers to a reduction in the airflow.

It is one of the most common breathing related sleep disorders.  It is characterized by episodes of blockage in the upper air pathway of the individual during sleep. Individuals suffering from obstructive sleep apnea hypopnea show presence of apneas or hypopneas along with nocturnal breathing disturbances such, snorting, snoring or pauses in breathing. These are also accompanied by daytime sleepiness and fatigue.

Categories based on severity-

  • Mild: Apnea hypopnea index is less than 15.
  • Moderate: Apnea hypopnea Index is between 15-30.
  • Severe: Apnea hypopnea index is more than 30.


l% -2% of children, 2%-15% of middle-age adults, and more than 20% of older individuals suffer from obstructive sleep apnea hypopnea.

5. Nightmare Disorder

Nightmares are frequent occurrences of extended, distressing and well-remembered dreams that mostly happen during the second half of the major sleep episode. It involves efforts to avoid threats to survival, security, or physical integrity. The individual on awakening from the terrifying dreams experiences rapid alertness. Nightmares are called disorders only when the prevent the individual from getting enough sleep and impairs the daily functioning.

Categories based on duration-

  • Acute: Symptoms of nightmares present for a period of 1 month or less.
  • Subacute: Symptoms of nightmares present for greater than 1 month but less than 6 months.
  • Persistent: Symptoms of nightmares present for 6 months or greater.

Categories based on severity-

  • Mild: Less than one episode per week on average.
  • Moderate: One or more episodes per week but less than nightly episodes.
  • Severe: Episodes nightly.


Prevalence of nightmares among adults is at least 6% monthly whereas prevalence for frequent nightmares is l%-2%.


An unstructured and imbalance sleep pattern can affect all areas of our life. It reduces our cognitive abilities, disturbs our mood and prevents us from working efficiently. We should attempt to maintain a healthy sleep hygiene in order to be capable to deal with the daily challenges of life.


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Written by Aastha Kothari

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Brinda S

Well written!

Nidhi Dahiya

Amazingly written

Amna Alim

very informative!

Stuti Jhaveri

Well written!!


Riya Rajkotiya

Well Written


very clearly written. its fascinating to see how during the rest phase the brain is highly functioning and operational. a particular stage of sleep is even called the paradoxical stage (REM sleep) as or body is paralyzed yet our brain is in movement. One suggestion is that it can be motioned that how or each person sleep requirements vary and how is relation to that the sleep disorders arises.
for example insomnia is the inability to sleep properly. its has no particular definition as the requirements vary from person to person.
another thing that can be mentioned is that non of these disorders are diseases, they are infact symptoms that arise due to the physical of mental conditions that you have very descriptively mentioned.

Disha Dhage


Disha Dhage

interesting topic

Disha Dhage

good job

Disha Dhage

will share this

Disha Dhage

amzing one

Disha Dhage


Jigyasa vashistha

Amazing content