It happens just as you’ve dozed off to sleep.
As you being to drift into dreamland, suddenly you are wrenched back to Earth by a sudden jolt.
It’s as if you’ve fallen off the kerb or tripped – and afterwards you feel wholly awake.
This is known as a ‘hypnic jerk’ and is actually an evolutionary adaptation that protected us from prey, says Jason Ellis, Professor of Sleep Science at Northumbria University.
Waking up one last time before we fall asleep allowed us to check for anything nearby that might eat us.
Or – if nodding off in a tree – it let us ensure our chosen bed for the night was actually safe.
But if this phenomenon is keeping you awake, there are things you can do to lower the chances of one happening.
Here, writing for The Conversation, Professor Ellis explains exactly how to manage the hypnic jerk, from avoiding exercise at night to taking magnesium….
That feeling when you are almost asleep only to experience a shocking jolt, as if you are falling is known as the hypnic jerk, according to Jason Ellis, Professor of Sleep Science at Northumbria University (file photo)
WHAT IS IT?
You climb into bed, get comfortable and cosy, start to feel your brain slowing down – and then suddenly you experience a shocking falling sensation.
It’s like you misjudged the number of stairs you were walking down, leaving your leg in mid air for just a bit longer than you expected. Not pleasant.
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This bedtime tumbling sensation is the phenomenon known as the ‘hypnic jerk’ and may sometimes be accompanied by a visual hallucination.
You may have heard it called a ‘sleep start’, the ‘hypnagogic jerk’ or the ‘myoclonic jerk’, but for the sake of sanity we’ll just stick with the former.
WHAT IS HAPPENING?
The hypnic jerk occurs when the muscles, usually in the legs (although they can be observed throughout the body), involuntarily contract quickly, almost like a twitch or spasm.
Although the reasons behind this are not that well understood, the evolutionary perspective suggests that it serves at least two important but interrelated functions, the former of which is still relevant today.
The hypnic jerk occurs because our bodies move from active and conscious motor control to a state of relaxation and bodily paralysis, one theory claims
First, this sudden awakening allows us to check our environment one last time, an opportunity to ensure that it really is safe to go to sleep by creating a startle-like response.
You might have accidentally dropped off somewhere dangerous, after all.
Another suggested evolutionary function is that it allowed us – or at least our early ancestors – to check the stability of our body position before we went to sleep, especially if we started to fall asleep in a tree.
The jerk would allow us to test our ‘footing’ before unconsciousness set in.
The other main theory suggests that the hypnic jerk is merely a symptom of our active physiological system finally giving in, albeit sometimes reluctantly, to our sleep drive.
The jerks can prevent people from falling asleep, leading to insomnia. Cutting out caffeine and lowering stress levels reduce the chances of a jerk occurring
Our bodies move from active and conscious motor control to a state of relaxation and bodily paralysis.
In essence, the hypnic jerk may be a sign of the eventual switch over between the brain’s recticular activating system and the ventrolateral preoptic nucleus.
The recticular activating system uses chemical messengers to aid wakefulness, while the ventrolateral preoptic nucleus uses messengers to reduce wakefulness and promote sleep.
WHEN JERKS GO BAD
Either way, although in most cases a normal and natural phenomenon, the hypnic jerk can be a rather disconcerting or frightening experience.
Avoiding exercising at night also makes it more likely you fall straight to sleep (file photo)
In extreme cases – whether in terms of frequency or the velocity and violence of the jerk – it can keep people awake, preventing them from falling asleep.
This can result in a form of sleep-onset insomnia.
As the hypnic jerk is related to motor activity, anything that is going to keep your motor system active at night is likely to increase the chances of you having one – and possibly even a more intense one, too.
As such, caffeine – or other stimulants – and/or vigorous exercise in the evening and high stress and anxiety levels at night should, where possible, be avoided as they are associated with an increased chance of a spontaneous hypnic jerk.
Other associations include being overtired or fatigued, sleep deprived or having an erratic sleep schedule.
Here, keeping a good regular sleep/wake pattern can help.
Finally, from a nutritional perspective, it has been suggested, albeit anecdotally, that deficiencies in magnesium, calcium and/or iron can also increase the chances of experiencing a spontaneous hypnic jerk.
That said, it has also been suggested that hypnic jerks can be evoked through sensory stimulation, during the sleep onset period, so ensuring that your sleep environment is cool, dark and quiet may be helpful in reducing the frequency and intensity of them.
There is actually very little research on the topic, presumably because it is largely seen as a normal phenomenon, making it difficult to suggest a definitive ‘treatment’.
However, we do know that as we get older the number of hypnic jerks we will experience should decrease naturally.
The main issue to consider here is whether the hypnic jerk is causing you or your bed partner a problem?
If it is, then it is time to see a sleep specialist. The difficulty is there are a number of sleep disorders, such as sleep apnoea, that have symptoms which mimic the experience.
And if all else fails, perhaps just blame the ancestors.