The sleeping baby strapped to my chest suddenly spasms and clasps me in a gesture I call “crabbing”. I stop to exclaim.
“Did you fall off your branch?” I ask my daughter.
The baby sleeps on.
But I know she will wake soon: sleep starts (or hypnic jerks) like this tend to happen when someone is falling to sleep or waking up, as their mind wrestles between consciousness and unconsciousness – like so many other sleep phenomena (e.g. sleep paralysis). And so far, experience has agreed with the science.
But what are these “sleep starts”?
According to a 2016 study[1], 60-70% of people experience them, a figure I have trouble believing, because sleep starts are a type of involuntary muscle spasm called myoclonic jerks – like hiccups. And who doesn’t experience hiccups? (Other sources think everyone gets them [2]). Because they happen when you’re asleep, it’s easy not to notice them. That sudden feeling of falling that throws you into ugly wakefulness just as you were drifting peacefully away? That. And along with the feeling of falling, impressions such as having blinding light in your face are common. Sometimes it can be purely “sensory” – the sleeper feels it but their body doesn’t move; other times, it’s imperceptible to the starter – a small body movement detected by somebody with the sleeper, like the occasional spasmic motions I see in my dormant cat. They can be detected with EEG (encephalogram).
“Did you fall off your branch?” I ask my daughter.
The baby sleeps on.
But I know she will wake soon: sleep starts (or hypnic jerks) like this tend to happen when someone is falling to sleep or waking up, as their mind wrestles between consciousness and unconsciousness – like so many other sleep phenomena (e.g. sleep paralysis). And so far, experience has agreed with the science.
But what are these “sleep starts”?
According to a 2016 study[1], 60-70% of people experience them, a figure I have trouble believing, because sleep starts are a type of involuntary muscle spasm called myoclonic jerks – like hiccups. And who doesn’t experience hiccups? (Other sources think everyone gets them [2]). Because they happen when you’re asleep, it’s easy not to notice them. That sudden feeling of falling that throws you into ugly wakefulness just as you were drifting peacefully away? That. And along with the feeling of falling, impressions such as having blinding light in your face are common. Sometimes it can be purely “sensory” – the sleeper feels it but their body doesn’t move; other times, it’s imperceptible to the starter – a small body movement detected by somebody with the sleeper, like the occasional spasmic motions I see in my dormant cat. They can be detected with EEG (encephalogram).
Known as “benign”, these amusing, irritating and bizarre performances affect us asymmetrically[3] – we’re not sure why. Theories go that the sleep start is (i) to help you not fall out of a tree as you relax, or is (ii) your body mistaking relaxation for falling out of a tree, or is (iii) due to changes in blood pressure and body tension as you relax. In fact, nobody knows why they happen, or what their evolutionary purpose might be. They’re mysterious. They happen more in babies than in adults. And, just like any other sleep condition, sleep starts are exacerbated by things like exercise, anxiety, alcohol and caffeine[4][5], but these are not causes – otherwise teetotallers would never get it, and it could be artificially induced with several large coffees. One group have shown success in treating it using tranquilisers[2] (a tranquiliser, though, that has been known to increase incidences of suicide in people who are already depressed).
For now, I’ll just accept my new status as my daughter’s branch, and keep laughing at my twitching cat.
To read more about weird sleep conditions, see our sleep article, or read our ghost story about sleep paralysis.
For now, I’ll just accept my new status as my daughter’s branch, and keep laughing at my twitching cat.
To read more about weird sleep conditions, see our sleep article, or read our ghost story about sleep paralysis.
why don't all references have links?
[1] Chiaro, Giacomo, et al. Hypnic jerks are an underestimated sleep motor phenomenon in patients with parkinsonism. A video-polysomnographic and neurophysiological study. Sleep Medicine 26 (2016): 37-44. doi: 10.1016/j.sleep.2016.07.011.
[2] Sathe, Harshal, et al. Hypnic jerks possibly induced by escitalopram. Journal of neurosciences in rural practice 6.3 (2015): 423. doi: 10.4103/0976-3147.158797.
[3] Fryer J. Hypnic reflex: A spinal perspective. J Sleep Disord Ther. 2014;3:5–6. doi: 10.4103/0976-3147.158797.
[4] Frenette E, Guilleminault C. Nonepileptic paroxysmal sleep disorders. Handb Clin Neurol. 2013;112:857–60. doi: 10.1016/B978-0-444-52910-7.00006-4.
[5] Lozsadi D. Myoclonus: A pragmatic approach. Pract Neurol. 2012;12:215–24. doi: 10.1136/practneurol-2011-000107.
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