Sleeping is a process that occurs in all mammals, and likely all vertebrates. When we are deprived of sleep we soon begin to crave it. Furthermore, if we are deprived of sleep for too long then it can sometimes be fatal.
Most people would likely assume that the brain becomes inactive when we are asleep, although this is not entirely the case. For instance, during REM (rapid eye movement) sleep the brain is about as active as someone who is awake. This is the stage of sleep where dreaming is said to occur. 
Sleep can be defined as a series of precisely controlled brain states. The sequence of these states is regulated by a set of specific brain-stem nuclei that disperse throughout the brain and spinal cord. 
What Are Sleep Disorders?
Sleep Disorders have a negative impact on an person’s ability to get a restful sleep. These disorders can have a profound impact on the individual’s health and overall quality of life.
In the United States, sleep disorders are becoming increasingly more prevalent. Around 40 million individuals living in America suffer from chronic sleep disorders, with an additional 30 million experiencing occasional sleeping problems. 
With these statistics in mind it is obvious that sleep disorders are a large health concern to the general public.
Sleep disorders range from being slightly bothersome to being potentially life-threatening. 
Most Common Sleep Disorders
There are a variety of different sleep disorders that exist. The most common sleep disorders are:
It is said that sleep apnea, restless leg syndrome, insomnia, and narcolepsy are the most prevalent sleep disorders. 
Sleep Disorder Symptoms
The symptoms associated with sleep disorders vary depending on the type of sleep disorder the individual is suffering from, and also the severity of the disorder.
The most common symptoms to look out for are:
- Difficulty in falling asleep/staying awake
- Difficulty in concentration
- Daytime fatigue
Sleep Disorder Causes
There are a wide variety of different disorders, diseases, and conditions that can cause problems with an individual’s ability to sleep. Sleep disorders often develop as a result to underlying health issues. Several of these causes include:
Allergies / Respiratory Problems
Stress & Anxiety
Studies have shown that genetics can play a role in the development of narcolepsy.  This is said to be very uncommon though as a majority of cases occur seem to occur sporadically, and without any genetic influence.
Types of Sleep Disorders
According to the third edition of the International Classification of Sleep Disorders (ICSD) there are seven main categories of sleep disorders.  Sleep disorders can therefore be classified into one of the following categories:
- Sleep-related breathing disorders
- Central disorders of hypersomnolence
- Circadian rhythm sleep-wake disorders
- Sleep-related movement disorders
- Other sleep disorders
- Purves D, Augustine G, Fitzpatrick D, et al. Sleep and wakefulness. In: Purves D, Augustine GJ, Fitzpatrick D, Hall WC, LaMantia AS, McNamara JO, White LE, eds. Neuroscience. Sunderland, MA: Sinauer Associates, 2004, pp. 659e685.
- American Academy of Sleep Medicine. International Classification of Sleep Disorders 3rd edn (American Academy of Sleep Medicine, 2014).
- Chabas, D., Taheri, S., Renier, C. and Mignot, E., 2003. The genetics of narcolepsy. Annual review of genomics and human genetics, 4(1), pp.459-483.
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