Many cases of narcolepsy are thought to be caused by a lack of the brain chemical hypocretin (also known as orexin), which regulates sleep.
This deficiency is thought to result from the immune system mistakenly attacking parts of the brain that produce hypocretin. However, a lack of hypocretin isn't the cause in all cases.
Immune system problem
Normally, antibodies are released by the body to destroy disease-carrying organisms and toxins. When antibodies mistakenly attack healthy cells and tissue, it's known as an autoimmune response.
In 2010 scientists in Switzerland discovered that some people with narcolepsy produce antibodies against a protein called trib 2.
Trib 2 is produced by an area of the brain that also produces hypocretin. This results in a lack of hypocretin, which means the brain is less able to regulate sleep cycles.
These research results may help explain the cause of narcolepsy in many cases, but it doesn't explain why some people with the condition still produce near-normal levels of hypocretin.
A number of factors may increase a person's risk of narcolepsy or cause an autoimmune problem, including:
Research is yet to confirm whether all of these play a role in narcolepsy.
Recent research has shown an association between the use of the flu vaccine, Pandemrix, which was used during the swine flu epidemic of 2009-10, and narcolepsy in children.
However, the risk is very small. Researchers estimate the chance of developing narcolepsy after receiving a dose of the vaccine is around 1 in 52,000 in the UK.
As a result of the findings, Pandemrix is no longer given to people under the age of 20.
Impact of narcolepsy on sleep
The total time someone with narcolepsy spends sleeping isn't necessarily different from that of people who do not have the condition. However, narcolepsy can significantly affect sleep cycles and decrease the quality of sleep.
Sleep consists of cycles of different brain activity known as non-rapid eye movement (NREM) and rapid eye movement (REM). During REM sleep, brain activity increases and dreaming may occur.
Normal sleep consists of three stages of NREM sleep at first, followed by a short period of REM sleep, with NREM and REM sleep then alternating throughout the night. During the latter part of the night, REM sleep is more prominent.
If you have narcolepsy, this pattern is much more fragmented and you may wake several times during the night. You may also experience REM sleep much earlier than normal after falling asleep, and may experience effects of REM sleep, such as dreaming and paralysis, while you're still conscious.