If you have ever been drifting off to sleep and all of a sudden, feel like you’re falling of a cliff and your whole body twitches, you are not alone. This is something experienced by roughly 70 percent of the population, and it’s known as called hypnic jerk.

A hypnic jerk, also known as sleep start or sleep twitch, is an involuntary muscle twitches that occurs as a person drift off to dreamland. This phenomena, which involves a total body experience where your arms, legs, or even your entire body twitches, generally happens when one enters the hypnogogic state – the transition between wakefulness and sleep.

Scientists are not exactly sure why hypnic jerks (twitching in sleep) occur. But, according to the latest episode of SciShow’s “Why Do We Jump In Our Sleep?” there are two main theories, based on neuroscience and evolution.

From neuroscience perspective:

We jump in our sleep because two different systems, the reticular activating system and the ventrolateral preoptic nucleus basically “battle each other” as we drift off to sleep.

The reticular activating system (RAS), also known as extrathalamic control modulatory system, is a network of nerve pathways just below the cerebral cortex. The system mediates the overall level of consciousness and when it is in full force, it activates alertness or arousal function and it essentially helps keeps you awake.

The ventrolateral preoptic nucleus (VLPO), also known as the intermediate nucleus of the preoptic area (IPA), is a  small cluster of neurons situated in the anterior hypothalamus, just above the optic nerves. This system, sometimes referred to as the “sleep switch,” influences your sleep cycle and  is active mostly during non-rapid eye movement sleep (NREM sleep).

So as you fall asleep, the VLPO system starts to take control from the reticular activating system. During this handoff, from one system to another; the alert part of your brain, RAS, sometimes strives to maintain control of your body – causing the muscles to twitch or move involuntarily. But, as you choose to sleep, the reticular activating system usually cedes control to the VLPO system and the hypnic jerks “eventually stop.”

“So these jerks are thought to be the result of a sleeping/waking war happening in your body each time you try to get some shut-eye,” says Micheal.

From evolution perspective:

Some scientists think that the ancient primate brain associated relaxation (or the beginning stages of sleep) with falling out of a tree. During the onset of sleep, the brain takes the relaxation wrongly as a sign of a threat that the primate is falling out of a tree, thereby causing the muscle to react quickly as possible. So, hypnic jerks were a way of waking up the sleeping primate quickly so they could prevent possible fall.

Most experts believe factors, such as anxiety, working out in the evening hours, fatigue, high caffeine consumption and irregular sleep schedules may increase the severity of hypnic jerks. But if you can cut back on these, you may experience fewer jerks.

There is no cure or official medical treatment for hypnic jerks. But whatever causes these, they’re nothing to worry about because even healthy people experience them. Well, there is another condition known as exploding head syndrome which you should be worried about.

Exploding head syndrome (EHS) is a psychological phenomenon in which a person hears load noises such as explosion, gunshot or thunder near one’s head. It is estimated that nearly 20 percent of the population suffer from this bizarre condition.

Have you experienced hypnic jerks lately? What is the worst nightmare you have ever had?