Have you ever gone to sleep at night and dreamt that you were falling, only to be abruptly woken by a sudden jerk of your body? This unsettling sensation is known as a hypnic jerk, and according to a 2016 study, 60 to 70 percent of people experience them.

The Stages of Sleep

Before diving into the cause of hypnic jerks, let's quickly review the stages of sleep:

Stage One:
This is the first phase when you start nodding off. It typically lasts a few minutes. During this period, your heartbeat, breathing, and eye movements slow, and your muscles begin to relax, though occasional twitches may still occur. Your brainwaves transition from the patterns of wakefulness to those seen in sleep.

Stage Two:
This is a period of light sleep that occurs before you enter deeper stages. Here, your heartbeat and breathing continue to slow, and your muscles relax further. Your body temperature drops, and eye movements cease. Your brain activity also slows, with occasional bursts of electrical activity.

Stage Three:
Stage three is essential for feeling rested and refreshed in the morning. Your heartbeat and breathing slow significantly, and it may be challenging to wake you up. This stage is also known as deep sleep.

REM Sleep:
Rapid Eye Movement (REM) sleep typically occurs about 90 minutes after falling asleep. During REM sleep, your eyes move rapidly from side to side, and your brain activity resembles that of wakefulness. Your breathing becomes faster and irregular, and your heart rate and blood pressure rise to levels similar to when you're awake. This is also when most of your dreaming occurs. You cycle through these stages multiple times throughout the night, with the length of each stage varying.

What Are Hypnic Jerks?

Hypnic jerks, also referred to as hypnagogic jerks or sleep starts, are involuntary movements that occur as your body transitions from wakefulness to sleep. While not fully understood, they tend to occur more frequently when you are sleep-deprived and trying to force your brain to engage in an activity. According to Rafael Pelayo, a sleep specialist at the Stanford Sleep Medicine Center, hypnic jerks happen when certain parts of your nervous system remain awake while others fall asleep.

Essentially, a hypnic jerk is a "misfire" of the nervous system, where your body receives mixed signals. They usually happen as you're moving from wakefulness into stage one of sleep. Typically, REM sleep occurs about 90 minutes after you fall asleep, but if you're sleep-deprived, you may skip stages two and three and move directly from stage one into REM sleep. Pelayo suggests that hypnic jerks act as a clear signal from the body, indicating that you need rest. "Nothing else is going to satisfy that urge," he explains.

Are Hypnic Jerks Dangerous?

Fortunately, no, hypnic jerks are not dangerous. Though they can be startling and uncomfortable, they are benign and don’t require treatment. Some people may feel anxious after experiencing a hypnic jerk and find it hard to fall back to sleep. If this happens, it can help to remind yourself that it’s harmless and there’s nothing wrong. This reassurance can help ease your mind and allow you to drift back to sleep.

Hypnic Jerks and Lack of Sleep

Although hypnic jerks are typically harmless, they can occur when sleep is unavailable, such as during a meeting or class lecture when you’re overly tired. In these situations, Pelayo offers a few tips:

• Focus on something more important than the urge to fall asleep.

• Make eye contact with the speaker to stay alert.

• Consider drinking coffee beforehand if you anticipate struggling to stay awake.

• Aim for seven to nine hours of sleep every night to avoid becoming overtired.

While hypnic jerks themselves are not harmful, they serve as a warning sign that you’re not getting enough sleep. If you notice them happening regularly, it may be worth examining your sleep habits and making adjustments to ensure you're well-rested.