Have you ever been falling asleep only to suddenly feel like you’re physically falling, followed by an abrupt body jerk that wakes you up? If so, you’re not alone. This sensation, known as a hypnic jerk, is surprisingly common, with a 2016 study finding that 60 to 70 percent of people have experienced it at some point. While it can be startling, understanding why it happens can make it a little less unsettling.

The Stages of Sleep

To understand hypnic jerks, it’s helpful to first look at the different stages of sleep. Our bodies go through a series of sleep cycles each night, transitioning through four main stages:

Stage One

The initial phase of sleep is short, lasting only a few minutes. As you start to drift off, your heartbeat, breathing, and eye movements slow down, and your muscles begin to relax. You might even notice small twitches as your body starts to unwind. During this stage, your brainwaves also begin to slow from their alert patterns.

Stage Two

In this next stage, sleep becomes a bit deeper, but it’s still considered light. Your body temperature drops, and your heartbeat and breathing slow even more. Eye movements stop, and brain activity decreases, though you may experience occasional bursts of electrical activity. This stage sets the foundation for the deeper sleep that follows.

Stage Three

This is the stage of sleep that leaves you feeling the most refreshed in the morning. During this phase, your heartbeat and breathing are at their lowest, and your muscles are completely relaxed. It’s difficult to wake up from stage three, as your body is deeply at rest.

REM Sleep

REM, or rapid eye movement sleep, begins about 90 minutes after you fall asleep. During REM, your eyes move rapidly from side to side behind closed lids, and your brain becomes highly active, similar to when you’re awake. Your breathing becomes quicker and irregular, and your heart rate and blood pressure increase. This is also when most dreaming occurs. Each night, your body cycles through these stages four or five times, with the length of each stage varying throughout the night.

What Are Hypnic Jerks?

Hypnic jerks, also called hypnagogic jerks or sleep starts, are sudden, involuntary muscle twitches that occur as you’re transitioning from wakefulness to sleep. They often happen during stage one of sleep, when your body is just beginning to shut down and relax. Though the exact cause of hypnic jerks isn’t fully understood, experts like Rafael Pelayo from the Stanford Sleep Medicine Center suggest that they’re due to parts of the nervous system staying awake while others begin to shut down.

Essentially, a hypnic jerk is like a miscommunication between different parts of your nervous system, causing your body to jolt as you start to fall asleep. When you’re sleep-deprived, your body may even skip stages two and three, moving quickly from stage one directly to REM sleep. Pelayo notes that hypnic jerks are a clear signal that your body urgently needs rest: “Nothing else is going to satisfy that urge.”

Are Hypnic Jerks Dangerous?

The good news is that hypnic jerks are not dangerous. They may be alarming in the moment, but they’re harmless and don’t require treatment. Some people may feel anxious after experiencing a hypnic jerk, making it harder to fall back asleep. If this happens to you, try to remind yourself that it’s a normal part of sleep and not a sign of anything wrong. Calming your mind with this reassurance can help you relax and get back to sleep.

Hypnic Jerks and Sleep Deprivation

Hypnic jerks are more common when you’re overtired, which is why they often occur during situations when falling asleep isn’t an option—like during a meeting or class lecture. When you’re trying to force yourself to stay awake, your body’s natural urge to sleep can trigger a hypnic jerk.

Pelayo offers some strategies for preventing hypnic jerks in situations where staying awake is necessary:

1. Stay engaged: Focus on something specific in the environment to keep your brain active.
2. Make eye contact: Locking eyes with a speaker can help maintain alertness.
3. Drink caffeine: Having coffee before an important meeting or lecture can help stave off sleepiness.
4. Prioritize rest: Aim for seven to nine hours of sleep each night to reduce the likelihood of experiencing hypnic jerks.

Why Hypnic Jerks Matter

While hypnic jerks themselves are harmless, they are often a sign that you’re not getting enough sleep. If you notice them occurring frequently, it’s worth considering whether you’re overly tired and in need of lifestyle adjustments. Consistent rest is crucial for both physical and mental well-being, so take hypnic jerks as a gentle nudge from your body to prioritize better sleep habits.

In short, hypnic jerks are just one of the many quirks of the sleep cycle. Understanding them can help make the experience less surprising, and it might even motivate you to get the quality rest your body truly needs.