This is why you have that weird dream where you're falling off a cliff
We’ve all had the sensation of falling asleep, only to have our body jerk awake with a dream about falling. It’s not a fun feeling, and often downright disturbing considering our sleepy state.
If you thought you were alone in experiencing this unpleasant dream sensation, rest assured: you aren’t. According Michael Aranda, host of the popular YouTube show SciShow, 70% of the population experiences these “sleep jerks,” or “hypnic jerks.” (The folks over the pond at BBC adorably refer to them as “sleep shudders.”)
Aranda explains in the video above that the most common theory behind the cause of these “hypnic jerks” is that the brain is engaged in a “sleeping-waking war.”
As writer Tom Stafford explains for the BBC,
Aranda describes in his video the battle between the reticular activating system (RAS) function of our brain, which is responsible for the sleep-wake cycle and controls how alert we are, and the ventrolateral preoptic nucleus (VLPO), which helps us fall asleep. According to Tehrene Firman at Good Housekeeping, the VLPO is sometimes called the “sleep switch.”
Basically, the VLPO controls sleepiness, and the RAS controls how awake we are. When we close our eyes and try to fall asleep, the sleepy part and awake part of our brain duke it out. As our brain gives in to sleep, the remaining daytime energy kindles and bursts out in random movements, often accompanied with a falling dream.
In other words, hypnic jerks are “the last gasps of normal daytime motor control.”
This isn’t the only theory in regards to our sleep shudders. Another theory suggests that evolution is responsible for hypnic jerks. Joseph Castro writes in Live Science that some scientists believe the sleep spasms are “an ancient primate reflex to the relaxation of muscles during the onset of sleep — the brain essentially misinterprets the relaxation as a sign that the sleeping primate is falling out of a tree, and causes the muscles to quickly react.”
Of course, we don’t live in trees anymore, so here’s hoping over time that if that is indeed the reason for our sleep jerks, they’ll eventually fade as our species progresses.
Until then, rest assured that those jerks are normal, and try to relax. Or, as Tehrene Firman advises her readers, “Just tell your RAS and VLPO to give peace a chance.”