If you’re someone who regularly experiences these startling awakenings you’ll be happy to know that there are steps you can take to avoid hypnic jerk. Lifestyle changes along with alterations to your bedtime routine can significantly reduce your chances of falling awake.
What Is Hypnic Jerk?
Some people experience them as a sudden tensing of their entire body — as if they were thrown onto the bed — while others feel an electric shock-like sensation.
These sudden starts are regularly experienced by 60-70% of people — well, as far as they are aware. Many times hypnic jerks are not strong enough to actually cause you to awaken, and so, you don’t remember them at all.
These muscle spasms occur during a specific point along our transition from wakefulness to sleep, called the hypnagogic state.
During this brief, transient state of consciousness our minds sift through different thoughts, emotions, and memories in a similar manner to that experienced in REM sleep: The difference being that you are, at least in part, aware. 
Additionally, they are associated with an increase in heart rate, breathing and sweating. 
While in the hypnagogic state, hypnic jerks may occur spontaneously or be initiated by external stimuli, such as a change in lighting or a sudden sound.
It’s common dream that you are tripping or falling when experiencing a hypnic jerk. This is due to dream incorporation: our brain’s ability to integrate external stimuli into our dreams, a process which demonstrates our mind’s amazing capacity for storytelling. 
Have you ever dreamt that a phone was ringing, only to finally awaken and realize that your cellphone is actually going off? That’s dream incorporation.
But what is it about our mind’s unique transition between being awake and asleep which causes these sudden muscle spasms?
What Causes Hypnic Jerk?
There are two prevailing explanations for why hypnic jerks happen:
- Natural Part Of Transition From State Of Alertness To Sleep: In this theory, hypnic jerks are thought of as an artifact of the brain wrestling between a state of alertness and sleep. As we drift off the sleep, remainders of daytime energy set off random bursts of brain electrical activity causing sudden muscle spasms.
- Evolutionary Reasons: An alternate explanation is that the cause of hypnic jerks can be traced back to our primate ancestors. As the body relaxes, the brain mistakenly recognizes this as a sign that we are falling out of a tree and causes our muscles to tense up.
According to both theories, hypnic jerks are a normal part of our physiology. However, some of us experience far more of these jarring awakenings than others. Are those individuals simply programmed to have more hypnic jerks? Or is there something they’re doing that’s contributing to their occurrence?
For a more in-depth explanation of these two theories check out this video from SciShow:
How Can I Avoid Hypnic Jerk?
While yes, hypnic jerks are a natural phenomenon that we all experience from time-to-time, there are certain elements which can increase the frequency and intensity of hypnic jerks.
If you find yourself regularly waking up with a start, ask yourself if any of these things may be the culprit:
- Caffeine and alcohol intake
- Heavy exercise close to bedtime
- Stress and anxiety
- Sleep deprivation and being overtired
- Uncomfortable sleep position
- Magnesium and calcium deficiency
As with most sleep related complaints, developing good sleep hygiene and following a bedtime routine will improve your overall quality of sleep and reduce the amount of hypnic jerks interrupting your slumber.
While hypnic jerks can be an annoying impediment to a good night’s rest, they are not a cause for worry. In fact, worrying about your hypnic jerks (thereby raising stress and anxiety) can actually increase their frequency.
Be proactive in your approach to reducing the amount of hypnic jerks you experience by carefully examining your bedtime habits and eliminating the factors that are contributing to their occurrence.