Approximately ​6 - 7 percent of the population in Singapore have experienced sleep paralysis.​​​

While some experience it once or twice in their lifetime, others may experience it regularly. The frightening condition, marked by breathlessness as well as the inability to move, scream or open your eyes while awake in bed, has been described across cultures worldwide.

For example, in China, it is called "gui ya shen" (ghost pressing on body). Similarly, in Malay, the phenomenon is known as “kena tindih” (being held down). In Mexico, it is referred to as "dead person on you". In Medieval times, folks believed they were being attacked ​by a succubus or incubus, a type of demon appearing in dreams.

“Knowing what triggers sleep paralysis and understanding how our sleep cycle works can reframe the experience and melt away the fear and terror associated with it,” says Dr Ong Thun How, Senior Consultant at the Department of Respiratory and Critical Care Medicine​ and Director of the Sleep Disorders Unit, Singapore General Hospital (SGH), a member of the SingHealth​ group.

What can trigger sleep paralysis

Although supernatural beliefs can intensify the terror felt during a sleep paralysis episode, they do not necessarily trigger it. The following factors, however, may increase your likelihood of experiencing sleep paralysis:

  • Mental distress
  • Lack of sleep or irregular sleeping hours​
  • Being a teenager or young adult
  • Sudden lifestyle change or variation in sleeping hours (due to jetlag for instance)
  • Use of drugs or certain medications to combat migraines and anxiety disorders
  • Other sleep disorders including narcolepsy and obstructive sleep apnoea*

How does sleep paralysis happen?​

To understand how sleep paralysis happens, you first have to learn a bit more about the sleep cycle.

The four stages of sleep in a sleep cycle

The average person goes through 4 to 5 complete cycles of sleep per night. Each cycle has four stages - 1, 2, 3 and rapid eye movement (REM). At stage 1, the brain’s sensory input begins to shut down but you may still recall sounds and sensations from your surroundings. At stage 2, your body starts to relax more and at stage 3, you are in deep sleep.

During the REM stage, your brain suddenly becomes very active, which gives you the ability to recollect vivid dreams. At the same time, almost all of your muscles are ultra-relaxed. This state of relaxation, called hibernation, prevents you from acting out your dream scenario (and unwittingly harming your bed partner).

An overlap between REM and waking stages of sleep

Sleep paralysis happens when there is an overlap between the REM and light stages of sleep. This means that your mind wakes up before the REM stage is complete. As such, you experience the inability to move or shout as well as breathlessness, and even panic. For some people, this feels like a hallucination.

Read on for tips to overcome sleep paralysis and when you should get help.

Ref: Q15