In other words, what we see, or eat and drink, our recall of past events, and how we are feeling are all possible causes.

Sometimes, as in most mammals, because of an evolutionary quirk it happens in response to a negative prompt, Palmer says. “The hackles rise in fear, intuitively or in premonition.” That’s because “the [fight or flight] neurotransmitters adrenaline and noradrenaline become tilted in the direction of fear or anger, or both”.

Do certain sounds make your blood boil? You could suffer from this

This shiver of unidentifiable dread has been referred to colloquially and in literature as the response to “somebody walking over your grave”, a phrase apparently coined hundreds of years ago to refer to British prisoners who were marched out of their cells to be hanged: their passage to the gallows meant walking across their own burial site.

But the feeling can also occur because of positive stimuli, Palmer says, in which case dopamine – a pleasure hormone – is involved.

Some research suggests experiences such as listening to rousing pieces of music can trigger a memory or an emotion to which the brain responds by signalling a muscle contraction. This creates the perception of an electrical shudder, or frisson. Apparently, those of us who experience such frissons (from the French, to thrill) share a common personality trait: an openness to new experiences.

Hong Kong ear, nose and throat specialist Dr Eric Tang explains that “when we try to hold back tears, there’s often a postnasal drip” that could irritate our pharyngeal mucosa, the site where air is warmed and humidified before reaching the lungs. This may give rise to the lumpy sensation which, Tang suggests, can be eased by drinking warm water or giving yourself a gently relaxing neck muscle self-massage.

That lump could also happen because anticipating tears prompts our fight-or-flight response, during which our systems demand high levels of oxygen. In an effort to take in more air, the nervous system sends an instant message to the glottis – the opening in your throat that channels air into your lungs – to stay open for as long as possible. So it opens wider than normal to allow in more air.

Of course, you aren’t aware of the widening glottis but you are aware of the muscle tension trying to keep it open even as your system needs to swallow. It’s the mixed muscle messages that create the sensation of a lump in the throat. As you calm down and your glottis returns to normal, the “lump” dissolves.

And what of that really annoying falling-off-a-cliff jolt just as you drop off to sleep? These are called hypnic – or hypnagogic – jerks, so-called because they occur in the hypnagogic state – that soft-edged transitional stage between being fully awake and fast asleep.

Kate Bridle, sleep expert and founder of Hong Kong’s Sleep HQ, says they’re quite common: up to 70 per cent of people experience them. Many never realise they have had a leg jolt, especially if it doesn’t fully wake them – or their sleeping partners. If a partner is awakened by a kick in the shin – and irritated – they may shake the innocent culprit properly awake to ask them to please stop thrashing about.

These twitches happen for any number of reasons, but Bridle says they happen usually when we are overtired and our body is trying to transition into deep sleep too quickly. “If you have them regularly they can be a sign that you are sleep-deprived. As far as we know, they are nothing to worry about.”

If they do bother you, she suggests focusing on your “sleep hygiene” to improve your sleep quality. If you are not getting enough sleep, try to make time for a little more each night – and take a complete caffeine detox for a few weeks, as it is thought that too much caffeine can also cause them.

Some research suggests that these jolts are a natural part of falling asleep and occur when nerves misfire during the transition from consciousness to unconsciousness.

Another theory suggests that – like the hackle-raising hair-on-the-back-of-the-neck sensation – they are an evolutionary hangover, an ancient primate response to relaxation. The brain misinterprets the relaxation as a sign that the sleeping ape is falling out of a tree, and triggers the muscles to quickly react, resulting in that falling feeling and starting-gun twitch in response.

We experience these things often without thinking – the lump in our throat as we stem tears is such a universal sensation, the starts that jerk us awake as we drop off to sleep so unremarkable, that we register them, or not, and then forget them.

To explore beyond these everyday sensations helps us understand more about the astonishing intricacies of the human body’s engineering.