By Mayo Clinic Staff. Most of the time fatigue can be traced to one or more of your habits or routines, particularly lack of exercise. It's also commonly related to depression. On occasion, fatigue is a symptom of other underlying conditions that require medical treatment.
http://www.mayoclinic.org/symptoms/fatigue/basics/causes/SYM-20050894
The excessive sleepiness may have a negative impact on the person's work, relationships and social life, and they may also: 1  have mental health problems, such as anxiety or depression. 2  have low energy.  be restless or agitated.
http://www.nhs.uk/Conditions/hypersomnia/Pages/Introduction.aspx
Excessive daytime sleepiness: A neurological disorder in which there is a sudden recurrent uncontrollable compulsion to sleep. Excessive daytime sleepiness is also known as narcolepsy. Automatic behaviors -- such as, for example, doing something automatically and not remembering afterwards how you did it.
http://www.medicinenet.com/script/main/art.asp?articlekey=10472
'Hypersomnia' means excessive sleep or sleepiness that interferes with everyday life. It can have many possible causes, including conditions such as narcolepsy, sleep apnoea or restless legs syndrome; severe sleep deprivation; depression; certain medications (such as tranquillisers); or drug and alcohol misuse.
http://www.nhs.uk/Conditions/hypersomnia/Pages/Introduction.aspx
Excessive daytime sleepiness is also known as narcolepsy. The condition is often associated with: 1  Cataplexy -- a sudden loss of muscle tone and paralysis of voluntary muscles associated with a strong emotion.  Sleep paralysis -- immobility of the body that occurs in the transition from sleep to wakefulness.
http://www.medicinenet.com/script/main/art.asp?articlekey=10472
1 The overnight sleep in narcolepsy is usually very fragmented and of poor quality, but people with idiopathic hypersomnia tend to sleep continuously through the night.  Short daytime naps in narcolepsy tend to be refreshing, but naps in idiopathic hypersomnia are more like long sleeps and are not refreshing.
http://www.nhs.uk/Conditions/hypersomnia/Pages/Introduction.aspx
Still other persons with the disorder may experience severe sleepiness or have severe cataplexy (with one or more episodes of cataplexy per day). The basic cause of narcolepsy is not known. It is not a fatal disorder in itself but it can lead to fatalities. For example, a narcoleptic may fall asleep while driving.
http://www.medicinenet.com/script/main/art.asp?articlekey=10472
Understand though, common doesn’t always mean normal. Let’s take a closer look at some of the factors that might lead a person to seek help for ES. Symptoms: Unremitting tiredness, inability to stay awake and/or maintain focus on tasks, irritability and/or lethargy. Causes: There are many causes of ES. As with all illness, it’s important to first find the underlying cause. Poor sleep quality – lying in bed all night, is no guarantee you are getting adequate sleep. Insomnia is one of the most common causes of daytime sleepiness. As a result, people take sleeping pills, in order to fall asleep. Of course, taking a pill to sleep has it’s own side effects (see below).
https://www.consumerhealthdigest.com/sleep-disorder/excessive-sleepiness.html
A number of tests can be carried out to assess your sleep and help identify any underlying cause. These are usually carried out at a specialist sleep centre. Two of the main tests used are: Polysomnography (a night time sleep test), which will help rule out sleep disorders such as narcolepsy or sleep apnoea.
http://www.nhs.uk/Conditions/hypersomnia/Pages/Introduction.aspx
Excessive daytime sleepiness is also known as narcolepsy. The condition is often associated with: Cataplexy -- a sudden loss of muscle tone and paralysis of voluntary muscles associated with a strong emotion.
http://www.medicinenet.com/script/main/art.asp?articlekey=10472
causes of severe excessive daytime sleepiness
The causes of severe excessive daytime sleepiness are narcolepsy, sleep apnoea or restless legs syndrome, severe sleep deprivation, depression, tranquilizers or drug and alcohol misuse. The causes of severe excessive daytime sleepiness are narcolepsy, sleep apnoea or restless legs syndrome, severe sleep deprivation, depression, tranquillisers, drug and alcohol misuse.