While it might seem like something out of a horror movie, this experience is actually a common condition known as sleep paralysis.

In conjunction with World Sleep Day today, FMT Lifestyle chatted with certified sleep disorder specialist Dr Rajveer Singh Saren on this phenomenon that affects up to four out of every 10 people.

He said that to understand sleep paralysis, one needs to know that there are two phases of sleep: rapid eye movement (REM) and non-REM.

REM is when one’s brain is more active and the body becomes relaxed and immobile. This stage accounts for about 20% of the sleep cycle, during which time one usually has vivid and complex dreams.

Non-REM, on the other hand, is the period during which the sleeper has fewer dreams; when they occur, they tend to be more conceptual and less vivid or emotional.

“Sleep paralysis is a type of parasomnia, which refers to unusual behaviours during sleep. It happens when you regain awareness going into or coming out of REM,” Rajveer explained.

“At this point, your brain has awakened but your muscles haven’t, leaving you unable to move except for your eyes.”

He added that this might also have a genetic component: if you have a family history of sleep paralysis, you’re likely to experience it, too.

As for why it affects some more than others, Rajveer cited reasons such as stress and sleep deprivation. Those with erratic sleep schedules – college students or shift workers, for example – might be more vulnerable.

Substance abuse or medication could also play a part: if you are a frequent alcohol drinker or are on certain types of medication, it could interfere with your sleep and lead to higher chances of paralysis, he said.

Furthermore, patients with sleep disorders such as narcolepsy and sleep apnoea are also prone to the condition.

Now for the juicy part of the conversation: what about those who associate sleep paralysis with the supernatural? Folklore from different cultures tends to influence the perceptions of sufferers, who relate the experience to being attacked by a jinn or having an entity press down on them in bed.

Rajveer believes it’s largely caused by the mind playing tricks owing to the state of being half asleep. The subconscious mind conjures up images or hallucinations as it tries to make sense of what’s happening.

“Of course, I can’t vehemently say that ghosts are not real,” he quipped, “but these are some of the scientifically proven facts I can give as to why sleep paralysis occurs.”

Rajveer also remembers the time he himself experienced sleep paralysis, while in his late teens. “I was terrified… and then I just fell back asleep after a while, since I couldn’t move anyway,” he laughed.

In all seriousness, Rajveer advises those who have recurrent sleep paralysis to get themselves checked to see if it is a symptom of an underlying health issue.

“Depending on the frequency or severity, we’ll ask about your sleep habits, factors that affect your sleep, and so on. Sleep tests will also be done,” he said.

All in all, the good doctor advises sufferers to try to get on with their day to day and enjoy life in moderation.

“Get adequate rest, keep a consistent sleep schedule, and reduce distractions such as electronic devices before bed. All these contribute to you having and maintaining good sleep hygiene, lessening the chances of sleep paralysis.”