I gave up worrying about health effects when I reached thirty. I designed and printed a card to all the doctors who'd said I wouldn't make thirty. Fifty years later I've forgotten when the hypnic jerks started, but I go straight back to sleep -- see below about my method of ensuring that I go back to sleep almost immediately. I don't know if hypnic jerks are linked to coffee or tea, but I drink a four-cup pot of tea with half a lemon or lime plus honey every day, and the same of mokka, a 3:1 mixture of cocoa and one heaped spoon of whatever instant coffee my wife buys at the supermarket.

For all I know the hypnic jerks may just be a result of angling your body horizontally when you go to sleep, rather than vertically. Or, perhaps more likely, they may be caused by hormones secreted in your brain to keep you sane by reminding you dreams are not real: dopamine, oxytocin, serotonin, and endorphins are so much the usual suspects of happiness that they are shorthanded as DOSE. Serotonin in particular has a wide variety of functions in the body as well as the brain, and both a shortage or an excess of serotonin in the body can produce undesirable effects.

One could speculate that vomiting, about which serotonin is known to send  messages to the nerve-ends, is a convulsive effect, rather similar to hypnic jerks, but don't take that as gospel as I haven't kept up with the literature.

I was prescribed amitriptyline for migraines, which are caused by damage to a mandibular nerve suffered during heart surgery when the surgeons had force my mouth open in a hurry. It's a medicine without a well-defined therapeutic map but for me it has always worked for whatever it was prescribed. The point of telling you all this is that, as a side effect of trying to do something about migraines, amitriptyline seems to keep the hypnic jerks at bay.

Or it may just be that my entirely unplanned diet of what I like to eat (chicken, oily fish and shellfish, cheese, avocado, fruit, yoghurt, red meat generally only once a week, mineral supplements to replace sunlight, rough brown rye bread, pasta, salami for a controlled intake of fat) works well to keep the DOSE well-balanced.

Medicine is a lottery...

But I know this stuff because I was taught it. I don't actually worry about the now rare (since I started taking amitriptyline) hypnic jerks, as I think it is far more likely a transient ischemic attack will get me, and I've never heard of a case where someone actually died of a hypnic jerk, which by definition is very brief. Not that I worry about TIA's either, which could start something not quite so "transient". Que sera sera.

If you have trouble going to sleep again after a hypnic jerk, it helps to have something else pre-chosen to focus your mind at the same time as you blank it off to the disturbance. You could mentally calculate the ratios in the Rohloff hub gearbox, for instance, or how many actually meaningful half steps you could get by inserting only one further chainring to the crankset. I try to improve the stress calculations in the chasses of cars I designed and (over-)built, without pencil and paper a near-impossible task never completed because I fall asleep almost immediately I flash up that particular spreadsheet in my mind's eye.

One final point: Your body's state isn't only an output of DOSE and lesser helper chemicals in your body and brain, your mood is also an input to the other regulators. If you make a point of being happy and carefree, the hypnic jerks might just feel so unwelcome, they jerk themselves up, leave you behind, and invade someone else's life.

Can 3 or 4 coffees a day be to blame?

I suffer(ed) from bouts of tachycardia. Heart rate suddenly increases, but seems weak, and fluttery. After a certain time, my heart seems to give one or two strong beats, then it goes back to normal. It happened more often when I wasn't getting enough exercise.

The cardiologist I saw when I was about 40 prescribed beta-bloquants and warned that it was dangerous not to take them. I put up with the beta-bloquants for about a week, but didn't like the side effects.

So I tried doing without tea and coffee and not taking the beta-bloquants. After the initial withdrawal symptoms, this has worked very well for me since. Thinking back, I first noticed having tachycardia at about the age of 10. Coincidentally (or not ?) this was about the same age I started drinking tea. From 10 to about 40 I used to drink either tea or coffee at virtually every meal, often in between meals as well.

Thanks both for your kind replies. I'm gonna mull over both to try and seek elucidation!

FWIW I believe these...happenings...began after I was prescribed the wonder drug Vioxx(for systemic arthritis)and which was later found out to be a 'poison'. Our American cousins died or received compo for taking this drug,but our own peoples here not a brass razoo. I was already halving my prescribed drug when I found out it was being withdrawn from the market. From this time in until I stopped taking it, my sleep jerks waned until now when and after I do a longish ride(and the ride is not long nor unduly strenuous,believe me!)

What caused me to come here was that the sudden jerk which awakes me is quite unsettling. Read that again! And having had it you are not inclined to go back to rest and sleep. I now dont get it at any other times. Sometimes,somewheres!,you meet a forum or a person who can offer advice or experience of a problem. Your two replies are two worth consideration. Thanks.

Finally,its getting in to see a receptive medical practioner. Then in having some belief in some. With apologies but from personal experience

The Mercury has superb steering and almost no one has ridden a 40, to date.

Almost no one?
They've sold hardly any in the year it's been available?

By any chance, have you ever been tested for sleep apnea?

It is a condition where breathing can start and stop multiple times a night, causing disturbed sleep or sudden wakefulness. There's a couple kinds, obstructive and central.

Migth be worth pursuing this with your doctors as a possible diagnosis. Given what you've written here, I am surprised they didn't mention the possibility.

As far as heart-related concerns, it is common for doctors to prescribe wearing a Holter heart monitor to record any anomalies during the period under study -- including sleep.

Best (and curious!), Dan.