Sleep paralysis is caused when hormones produced by the body to help you sleep do not wear off as you wake up.
This means that you remain temporarily paralysed but conscious.
To understand better what causes sleep paralysis, it is useful to know what usually happens when you are asleep.
Sleep occurs in cycles and each cycle is split into two phases – rapid eye movement (REM) sleep and non-REM sleep.
The brain is very active in REM sleep and most dreams occur at this stage of sleep. [1
] Also, during REM sleep the body is paralysed, apart from the movement of the eyes and diaphragm (the main muscle used in breathing).
] The paralysis is thought to occur to prevent you acting out the actions in your dreams.
Sleep paralysis occurs when the normal muscular paralysis of REM sleep temporarily continues after you have woken up.
Certain factors make you more likely to get sleep paralysis:
 age – it is more common in teenagers and young adults
 sleep deprivation – sleep paralysis is more common in people who do not get enough sleep
 irregular sleeping patterns – people with irregular schedules or who work shifts are more prone to sleep paralysis
 narcolepsy – some people with narcolepsy (a sleep disorder where you suddenly fall asleep at inappropriate times) also experience sleep paralysis
 family history – you may be more likely to have sleep paralysis if another member of your family also has it; however, this is an area where further research is needed
The main symptom of sleep paralysis is a temporary inability to move or talk.
 The paralysis usually happens as you are waking up, but it can also sometimes happen when you are falling asleep.
 Not being able to move or talk can be very frightening, particularly as you will be completely conscious throughout the experience.
During an episode of sleep paralysis, you may also experience a very real sensation that there is someone else in the room with you.
These type of hallucinations are a fairly common feature of sleep paralysis, although they do not occur in every case.
 The length of time that you are unable to move for can vary from a few seconds to several minutes. After this, you will be able to move and speak as normal.
 Immediately after an episode of sleep paralysis you may feel unsettled and anxious.
However, the condition does not pose a risk to your overall health.
Many people only experience sleep paralysis once or twice in their life. If it happens several times a month or more regularly, it is known as isolated sleep paralysis.
Treating sleep paralysis
Ensuring you get enough sleep and improving your sleeping environment will help if you have sleep paralysis. In severe cases, medication may be recommended.
 Sleep paralysis is more common in people who are sleep deprived, so getting enough sleep may help reduce the number of episodes of sleep paralysis. Most adults need 6-8 hours of sleep each night.
Keeping to a regular sleeping schedule, where you go to bed at roughly the same time each night and get up at the same time each morning, can also help.
Tips for improving your sleeping habits include:
 creating a restful sleeping environment that is quiet, dark and not too hot or cold
ensuring your bed is comfortable
exercising regularly (but not too close to bedtime)
cutting down on caffeine
not eating or drinking alcohol before bedtime
giving up smoking (if you smoke) because nicotine is a stimulant
If your sleep paralysis is particularly troublesome, you may be prescribed a short course of antidepressant medication, such as a tricyclic antidepressant (TA), typically clomipramine.
 Antidepressants affect mood and are usually used to treat depression, but are also sometimes prescribed to treat severe sleep paralysis.
The medication is thought to work by altering the amount and depth of REM sleep. This should prevent the temporary paralysis when you wake up or fall asleep, and it should also help reduce any hallucinations you may have.
You may be advised to take the medication for a month or two to see whether it improves your symptoms.
Possible side effects of TAs can include:
These side effects should ease after 7-10 days as your body starts to get used to the medication. You should visit your GP if the side effects have not eased after this time.
Read more about the side effects of TAs.
Sleep paralysis can sometimes be a symptom of another sleep disorder called narcolepsy, which causes severe daytime sleepiness and an inability to stay alert for more than a few hours.
Although there is no cure for narcolepsy, the condition can usually be managed with medication.
A number of lifestyle adjustments may also help, including:
 taking frequent brief naps during the day
sticking to a strict bedtime routine where you go to bed at the same time each night
ensuring you get at least eight hours of sleep every night
avoiding stressful situations, eating a healthy, balanced diet and taking regular exercise (but not too close to bedtime)
Read more treatment advice for narcolepsy.