Why You Jolt Awake Just as You’re Falling Asleep, According to Sleep Experts

Sleep specialists say these nighttime jolts are usually harmless, even if they leave you wide awake and rattled. Here's what's going on behind the scenes and how a few lifestyle changes may help keep them at bay.

You're snuggled up in bed, finally drifting off after an exhausting day, when out of nowhere your entire body tenses up and jerks you awake as if somebody just shook you — and it all happens within seconds.

What you've just experienced is a hypnic jerk.

Also known as a sleep start, the phenomenon can come with some vivid sensations.

"Sometimes there's an image that you're falling, or missing a step, being tossed a ball they needed to catch, etc., and that corresponds with the phenomenon. For some, there is an actual sense of falling," explains Dr. Chris Winter, a neurologist and sleep specialist.

Some people even experience visual or auditory stimuli, such as flashing lights and stars or clicks and bangs. Sleep starts can happen to pretty much anyone, regardless of sex or age, and drifting back off afterward can be frustratingly difficult, especially if they happen often or several nights in a row.

If you want to tackle them, it helps to first understand why they happen. The scientific term for the phenomenon is hypnic myoclonus, with "hypnic" referring to "hypnagogia," a word used to describe the transitional state between wakefulness and sleep.

Dr. Charlene Gamaldo, a neurology professor at Johns Hopkins School of Medicine and medical director of the JH Center for Sleep and Wellness, says hypnic jerks may involve just one muscle or a rapid-fire series of twitches and spasms.

"It typically involves a single contraction of a limb or synchronized contraction of multiple limbs during the sleep transition," she says.

These muscle movements are most likely to strike as you first begin to fall asleep and during the light stage of sleep that immediately follows.

Twitching, jerking, or feeling as though you're falling or floating while asleep can happen to people who are otherwise healthy. For most, these sensations are generally considered a normal part of the sleep cycle.

"Most times, they are unnoticeable and mild, but other times, they can wake us out of sleep," says Dr. Funke Afolabi-Brown, sleep medicine physician and founder of Restful Sleep MD. "Hypnic jerks usually occur at sleep onset. As we cycle through sleep stages and have an arousal at night, hypnic jerks can also occur then."

As with many processes in the human body, hypnic jerks still hold some mystery, but experts have come up with a few ideas about what causes them.

One theory suggests that the stage of sleep in which they often occur is light enough that your brain may mistake it for wakefulness — while also noticing that your muscles aren't moving.

In response, your brain sends a message to your muscles, almost like a quick status update, rousing them or keeping them active and reactive as a means of protection. Chemical messengers called neurotransmitters then relay that signal from your nerve cells to your muscles, latching onto the protein cells there.

Once that connection is made, the muscle cells get their cue to spring into action, and your muscles start to move. "The result is likely that feeling of movement, falling or a jerk as your muscles are stimulated," Reena Mehra, MD, MS, a sleep disorder specialist, says.

Afolabi-Brown notes that some research has traced the hypnic jerk reflex to the same part of the brain responsible for our startle response.

"Brain-wise, the cause of hypnic jerks is not completely understood but felt to be related to signals sent from our brain stem, down to a relatively unstable nervous system during the wake to sleep transition," she says.

As mentioned, sleep starts are a normal part of the sleep cycle and rarely a cause for concern. Still, certain factors can make them more frequent. "Stress can worsen hypnic jerks," Dr. Sonja Schuetz, a neurologist, says.

She explains, "There are also several other factors that can increase the frequency of hypnic jerks — for example, increased caffeine intake, intense physical exercise, or sleep deprivation."

Winter says a few simple tweaks can help cut down on hypnic jerks while also supporting a healthier lifestyle overall.

"Get more sleep, make your sleep schedule more regular, avoid caffeine, and work on lowering stress," he says. "Sometimes medications can be prescribed, but this is pretty rare. I think when they are increasing in frequency or intensity or are interfering with sleep quality, a professional should be involved."