Have you ever felt like you were falling while drifting off to sleep, only to be jolted awake by a sudden body jerk? If so, you’re not alone. This strange sensation is called a hypnic jerk, a common occurrence that affects 60 to 70 percent of people, according to a 2016 study. Though startling, it’s a typical part of transitioning from wakefulness to sleep.
Understanding the Stages of Sleep
To grasp why hypnic jerks occur, it’s helpful to understand the stages of sleep. Each night, our bodies go through a series of sleep cycles, each consisting of four distinct stages:
Stage One
This is the initial phase of falling asleep, which lasts just a few minutes. During this light stage, your heartbeat, breathing, and eye movements slow down, and your muscles start to relax, often with slight twitches. Your brainwaves also shift from their active, wakeful patterns to slower frequencies.
Stage Two
In stage two, you enter a slightly deeper state of sleep. Your heart rate and breathing slow further, body temperature drops, and eye movements come to a stop. Although brain activity decreases, you may experience brief bursts of electrical activity.
Stage Three
This stage is critical for waking up feeling refreshed. It’s the deepest stage of non-REM sleep, where your heartbeat and breathing reach their lowest rates, and your muscles are completely relaxed. It can be challenging to wake up during this phase.
REM Sleep
REM (rapid eye movement) sleep begins about 90 minutes after you fall asleep. During this phase, your eyes move rapidly behind your eyelids, brain activity spikes, breathing becomes faster and irregular, and your heart rate and blood pressure increase to levels similar to wakefulness. This is the stage where most dreams occur. Throughout the night, you cycle through these stages about four or five times, with each cycle varying in length.
What Are Hypnic Jerks?
Hypnic jerks, also known as hypnagogic jerks or sleep starts, are involuntary twitches or muscle spasms that occur as you transition from wakefulness to sleep, typically during stage one. While the exact cause of these jerks isn’t fully understood, they are believed to be linked to the nervous system, which remains partially alert while the rest of your body is shutting down for sleep.
Rafael Pelayo, a sleep specialist at the Stanford Sleep Medicine Center, explains that hypnic jerks happen because some parts of the nervous system are still awake while others are entering sleep. In a sense, a hypnic jerk is a misfire caused by the nervous system sending mixed signals to the body. They are more common when you are overtired or trying to force yourself to stay awake.
When you’re severely sleep-deprived, your body may skip over stages two and three of sleep, going straight from stage one to REM. In such cases, hypnic jerks are a clear signal from the body indicating that it urgently needs rest. According to Pelayo, “Nothing else is going to satisfy that urge.”
Are Hypnic Jerks Harmful?
While hypnic jerks can be startling, they are not harmful. They are benign and do not require medical treatment. However, the sudden jolt can sometimes cause anxiety or make it difficult to fall back asleep. If you find yourself unable to settle down after experiencing a hypnic jerk, try to remind yourself that it’s a normal part of the sleep process. Knowing that there’s nothing wrong may help calm your mind and allow you to drift back to sleep more easily.
Hypnic Jerks and Sleep Deprivation
Hypnic jerks are most common when you’re overly tired. They can even occur in situations where sleep isn’t an option, like during a dull meeting or class lecture. In these cases, your body’s need for sleep is so strong that it tries to enter the initial sleep stage despite the environment, causing the sudden jerk.
Pelayo offers some practical advice to prevent hypnic jerks in situations where staying awake is important:
- Stay engaged: Focus on something specific about the meeting or lecture to keep your brain active.
- Make eye contact: Keeping your eyes on the speaker can help you maintain alertness.
- Drink coffee: Caffeine can help stave off sleepiness and reduce the likelihood of experiencing hypnic jerks during daytime fatigue.
- Get adequate rest: Aim for seven to nine hours of sleep each night to reduce the risk of being overtired.
Hypnic Jerks as a Wake-Up Call
While hypnic jerks are not a serious health concern, they can be a sign that you aren’t getting enough sleep. If you notice them happening frequently, it may be time to assess your sleep habits and figure out why you’re feeling overly tired. Consistent sleep deprivation can affect your overall health and well-being, making it essential to address any underlying issues contributing to your lack of rest.
In summary, hypnic jerks are a natural response to sleep deprivation, signaling that your body is exhausted and needs rest. Though they can be surprising, they’re usually harmless and don’t indicate any serious health problems. So, the next time you’re jolted awake by a hypnic jerk, take it as a cue to prioritize better sleep habits.
