You may have found yourself in this scene: you are relaxing, almost drowsy, when suddenly you feel a startle, as if the body is rushing downwards. Immediately your heart shoots up, and you feel a brief shock that wakes you up or interrupts your sleep. This phenomenon is much more common than you might think, and although it is disconcerting, it does not usually represent danger.

Specialists call this reaction “hypnagogic spasm” or “sleep shaking”.
These jerks are sudden muscle contractions that occur during the transition from wakefulness to deep sleep. They usually appear right at the beginning of the sleep process.

Why does this sensation of falling occur?

Although science has not come up with a single definitive explanation, there are solid theories that help to understand why this happens:

• One explanation suggests that when the body relaxes very quickly when falling asleep, the brain can “interpret” that sudden relaxation as a loss of control or body support. In response, it triggers a muscle contraction, which manifests as the sensation of falling.
• Another hypothesis takes our ancestors as a reference: when they slept in unstable or vulnerable conditions (for example in trees or rocks), a reflex to protect themselves from a real fall could have remained in our nervous system as a vestige.
• It is important to note that this phenomenon occurs mainly at the onset of sleep, not during the deepest phases. This strengthens the idea that it is linked to the transition between wakefulness and sleep.

Factors that can increase the frequency of these shocks

Although hypnagogic spasms can appear isolated and for no apparent reason, several factors can increase their appearance:

• Extreme fatigue: When the body is very tired, the process of “shutting down” the system occurs more abruptly, and the brain can react more intensely.
• Stimulants: caffeine and nicotine activate the nervous system, hindering the natural transition to sleep.
• Stress and anxiety: an agitated mind combined with a body that wants to relax creates the right scenario for these shocks.
• Stimulant medications: Some medications for conditions such as ADHD can increase the likelihood of these jerks.
• Irregular sleep rhythm: sleeping and waking up at very variable times affects sleep cycles and can promote these episodes.

Is this something I should be concerned about?

In the vast majority of cases, no. Feeling like you’re “falling” in your sleep or experiencing a sudden isolated muscle contraction doesn’t indicate a serious problem.
However, it is advisable to be attentive if this phenomenon becomes very frequent, or is accompanied by other symptoms such as:

• Persistent tremor during the day.
• Muscle aches that have no other apparent explanation.
• Constant difficulty falling asleep or staying asleep.
• Recurrent abrupt awakenings.

In these cases, it is advisable to consult a doctor or a sleep specialist, because although isolated spasms are usually benign, they could be related to myoclonus or other neurological disorders in more complex contexts.

What can be done to reduce its frequency?

The good news is that with some changes in habit you can considerably reduce the appearance of these startles when sleeping. Here are some practical recommendations:

• Avoid caffeine and nicotine for six hours before bedtime.
• Turn off screens (phone, tablet, TV) at least 30 minutes before bedtime, as blue light inhibits the production of melatonin, the sleep hormone.
• Create a relaxation ritual: a warm bath, light reading, meditation, or leisurely breathing help the body gradually enter the restful state.
• Set set times for sleeping and waking up. A regular rhythm strengthens the natural sleep cycle.
• Practice mindful breathing techniques or gentle yoga before bed. These activities help calm the mind and make it easier for the body to “rev down.”

The best strategy is to improve sleep hygiene habits — avoiding stimulants, maintaining a regular schedule, unplugging screens, and relaxing — to reduce their occurrence. And if it becomes frequent or is accompanied by other symptoms, do not hesitate to talk to a specialist.