Hypnic Jerk

You are just about to fall asleep when your body jerks, waking you up. This unexpected contraction of your muscles is called a hypnagogic jerk, or hypnic jerk, for short. The term hypnagogic refers to the stage between awake and asleep, the time when the jerks happen. They are associated with the shift that occurs when transitioning from fully awake into the lightest level of sleep, non-REM sleep. They don’t happen in the deeper state of REM sleep.

The hypnic jerk is a type of myoclonus or involuntary muscle twitch, sometimes called a sleep start or a sleep twitch. These muscle twitches don’t follow a predictable pattern, and are very commonplace with 60-70% of people reporting they experience them regularly.

What Is a Hypnic Jerk?

A hypnic jerk is essentially a startle response, which happens most often just as you are falling asleep. It is commonly described as a feeling of falling, that may or may not be accompanied by a dream or visual image. Some people report feeling like they are falling out of bed, falling off of a curb, falling out of a tree, or falling off a cliff. Others report a feeling of falling into a void. A smaller percentage of people describe a hypnic jerk episode as feeling like they are “shocked” awake. No matter the perceived experience, the body responds to the hypnic jerk with an accelerated heart rate, intensified breathing, and sometimes sweating.

The strength of a hypnic jerk can range from very mild and not even noticeable, to strong enough to fully wake you up. Hypnic jerks are not considered a comorbid sign of any other disorder; however, they may be related to certain causational factors.

Hypnic Jerks seem to occur regularly in babies and young children, who have repetitive jerking movements while sleeping. The American Academy of Sleep Medicine has found some evidence that they increase with age, but conversely others studies have shown a decrease in frequency as we grow older. More conclusive research is still needed on this point.

What Causes a Hypnic Jerk?

As of yet, there are no definite conclusions as to what causes a hypnic jerk. There seems to be a number of correlative factors that increase likelihood and frequency, and a number of theories as to what is behind the jerks. Correlative factors are all lifestyle related and tend to increase hypnic jerks. Examples include:

• High stress levels
• Anxiety
• Too much caffeine
• Evening exercise
• Sleep deprivation
• Alcohol

There are a number of theories as to the cause of the hypnic jerks. The seven most common explanations are as follows:

• Normal Body Response: As your body relaxes and breathing slows, muscle tone lowers and this natural transition at the time of sleep can cause a muscle jerk.
• Primate Response: It is believed that we might have an innate jerk response leftover from when we were primates sleeping in trees. This response let us know when we were falling out of a tree, but is no longer needed.
• Sleep Stage Transition: Some theorists postulate that the jerk happens as a part of the body transitioning from awake to stage 1 of non-REM sleep.
• Brain Perception: This theory understands the hypnic jerk as a natural response by the brain. When the brain perceives the body relaxing, it can have a momentary panic that signals the body to wake up.
• Heavy Snoring: The muscle jerks may be in response to lack of breath that can happen with heavy snoring.
• External Stimuli: This understanding associates the hypnic jerks with noise or movements happing in the environment around the sleeper. They are subconsciously perceived and wake the person with up causing a jerk.
• Neurons Misfiring: When protein builds up or other factors cause the brain neurons to misfire they may cause an associated muscle jerk.

Preventing Hypnic Jerks

Hypnic jerks are nothing to be concerned about and nothing needs to be done about them. However, if they are happening frequently, disturbing your sleep, or you feel concerned about them, consult your doctor for input and possibly sleep medication. There are some simple fixes that do seem to lower the intensity and frequency of hypnic jerks like:

• Practicing good sleep hygiene
• Going to bed very relaxed
• Avoiding caffeine in the second half of the day
• Limiting alcohol
• Leaving strenuous exercises for the morning 

Summary

A hypnic jerk is a common muscle twitch that can occur as you fall asleep. It may be caused by a number of natural body processes or it may be a leftover safety response from when we were primates. In general, hypnic jerks are not considered harmful and do not need treatment.