This is why you can experience sleep paralysis after a big night out

Sleep paralysis causes sufferers to experience terrifying hallucinations and renders them unable to speak or move, whilst being completely aware of their surroundings.

For those of you lucky enough to have never experienced sleep paralysis, the best way to describe it is like those horrible recurring nightmares you had as a kid, where you'd scream at the top of your lungs but no noise would come out.

Whilst less than eight per cent of the general population have suffered from sleep paralysis, 28 per cent of students have reported experiencing it. It can often occur due to the lack of sleep or irregular sleep patterns, and often people experience sleep paralysis after festivals or a big night out.

What is sleep paralysis?

According to the NHS definition, sleep paralysis is the "temporary inability to move or speak that occurs when you're waking up or falling asleep."

They list the main symptom as being "completely aware of your surroundings but temporarily being unable to move or talk."

But other symptoms may include: finding it difficult to take deep breaths, as if your chest is being restricted, feeling as if you're being choked, and hallucinating or having the sensation that there is something in the room with you.

Whilst it isn't harmful and should pass within a few minutes, it can be extremely frightening.

Some research has suggested that it might be linked to deeper psychiatric or health problems, but in most cases it is simply a sign that your body is not moving smoothly through the stages of sleep.

It is also referred to as "the night hag" or "old hag syndrome", which is the name given to a supernatural creature, used to explain the phenomenon of sleep paralysis.

Why does sleep paralysis happen?

Whilst you're sleeping, your body alternates between rapid eye movement (REM) sleep, and non-rapid eye movement (NREM) sleep. During NREM the body relaxes and restores itself. Once this has occurred your sleep shifts to REM. REM is the stage of sleep when your brain is most active and when dreams normally occur.

Sleep paralysis happens when REM occurs whilst you're awake. Your body is temporarily paralysed, with the exception of the eyes and the muscles required to breathe, most probably to stop you acting out your dreams and injuring yourself.

This is why you're aware of your surroundings, feeling as if you're awake, but you are unable to move or speak because your muscles are essentially switched off.

It's still quite unknown why sleep paralysis actually occurs, but research has suggested it could be due to a number of factors, including: not getting enough sleep or irregular sleeping patterns, family history, and even sleeping on your back.

It's usually identified in the teen years, but anyone can develop it. In fact, some research suggests that up to four in 10 people suffer from regular sleep paralysis.

There are actually two different types of sleep paralysis

The first type of sleep paralysis is called 'Hypnompompic' sleep paralysis. This is the one described earlier, which occurs during REM, and is the most common.

But there is also a rarer form called 'Hypnagogic' that occurs as you fall asleep and your body relaxes. Usually you are less aware so you don't notice the change, but if you become aware as you fall asleep you might find yourself unable to move or speak.

And there are three different types of hallucinations

The types of hallucinations that occur during sleep paralysis fall into three distinct categories:

1) Intruder Hallucinations: you might feel the presence of a threatening presence or individual.

2) Incubus Hallucinations: you may feel someone pressing down on your chest or trying to choke you.

3) Vestibular-motor Hallucinations: you might feel as if you're floating, flying or moving. This can feel like an out-of-body experience.

The most common form of sleep paralysis is the intruder hallucination.

How to stop sleep paralysis

There's no cure for sleep paralysis, but there are things you can do to lessen the chances of it occurring.

Improving your sleep habits and/or sleeping environment can prevent it from happening as regularly.

It might help to make sure you get enough sleep (six to eight hours is ideal), form a sleeping pattern (going to bed and getting up at regular times), sleeping in a comfortable, dark and quiet environment that's the right temperature, and sleeping in positions that aren't on your back.

Other factors that might help include: not eating big meals, not smoking, not drinking alcohol or caffeine before bed, and getting regular exercise.

It's advisable to see a doctor if the symptoms are so severe that they're making you anxious or preventing you from sleeping, as there are some medications which can help.

Related stories recommended by this writer:

• Sleep Paralysis: The unspoken mental health issue

• Heavy chest, breathing issues, and hallucinations: What it’s like living with sleep paralysis

• A scientist explains why you have weird lucid dreams after a festival