What causes a a single, violent, whole-body "twitch" while falling asleep?
August 17, 2006 3:17 AM   Subscribe

What causes a single, violent, whole-body "twitch" while falling asleep? This happens to me frequently, but irregularly. After going to bed, closing my eyes, and relaxing for some time, out of nowhere I'll experience a very strong, but very brief, muscular "jerk" involving what feels like the entire body.

Normally, this will jolt me back to being fully awake, and often wakes my wife as well. When it does wake me up, a have the sense (I feel that I know) it happened just at that very moment I "officially" fell asleep—almost as if my mind "popped the clutch" while shifting from awake-but-relaxed to asleep. The sensation is nearly identical to when someone sneaks up behind you and startles the Hell out of you as a joke. As far as I can tell, there is no common circumstance preceding this "twitch". Is there a name for this phenomenon? Is it common? And, most interestingly, what's happening neurologically or physiologically to cause it?
posted by CodeBaloo to Health & Fitness (25 answers total) 5 users marked this as a favorite
Best answer: Hypnic Jerk
posted by Leon at 3:25 AM on August 17, 2006 [1 favorite]

Response by poster: That's it. Three cheers for the hive mind -- 8 minutes, asked to answered!

Now that I know what it is, I can look into existing research... I find the phenomenon fascinating.
posted by CodeBaloo at 3:31 AM on August 17, 2006

Were you guys talking about me?

...sorry couldn't resist. This the best sockpuppet/band name ever.
posted by Hypnic jerk at 5:33 AM on August 17, 2006

Is this normally accompanied by a flash dream? When I have had this it's normally a very brief and extremely visual of falling. Last time it happened I visualised falling down stairs, and as I braced my hands out in front of me and hit the ground... WHAM, I woke up with a real shock.

Odd how they seem to precede the shock. I also once had a series of these. I visualised racing down a hallway, slamming into the door at the end and bursting into.... the same hallway, racing down it and slamming into the door, and bursting into the same... etc. I got about five major jolts out of that. Nasty.

Okay, now I checked out handee's second link and see the dreams referenced.
posted by tomble at 5:52 AM on August 17, 2006

I'm usually walking down the sidewalk, and then suddenly trip!

Or floating gently, then suddenly hit the ground!
posted by muddgirl at 6:22 AM on August 17, 2006

AKA hypnagogic jerk as well.
posted by gramcracker at 6:28 AM on August 17, 2006

I once read a hypothesis, in a reputable journal (can't recall the name/issue), that it's a hold-over from our simian history, derived from the "quick, grab the tree before you plunge to your death" impulse.
posted by Merdryn at 6:55 AM on August 17, 2006

This happens to me apparently every night, often several times. I first noticed it when I was about 12 I think and it often coincides with me getting a fright or shock in a dream. First time it happened and it woke me I thought I'd gotten an electric shock and spent 10 minutes hunting around my bed trying to figure out what had shocked me.

Typical dreams when it occurs and wakes me would be falling, having something hit me or receiving electric shocks.

As for the "grab the tree" hypothesis, this is perhaps borne out by the fact that I apparently crush my girlfriend if I'm holding onto her when this happens. Otherwise it's mostly just my legs & back that twitch.
posted by polyglot at 7:37 AM on August 17, 2006

Ha! I do the same thing, but didn't know what it was... Thanks! The only thing is, I didn't know I did it until my girlfriend pointed it out. Most of the times I do it are when I fall asleep for only a second or two (like when I'm watching a movie), or when I'm in class (the teachers always seem to notice that guy that twitches when he falls asleep... dang), with mine though, no dreams accompany the twitch.
posted by tdreyer1 at 8:13 AM on August 17, 2006

Anyone else do this every night?

No dreams, no falling sensation, just a couple jerks (sometimes forcefully) every now and again every night after falling asleep?

Doesn't wake me up, and I have no idea I'm doing it.. (In fact, wouldn't know about it, if I hadn't heard about it from every ex-girlfriend in the past 5 years)..
posted by 4months at 8:27 AM on August 17, 2006

Does anyone else HATE these? I thought my husband was weird because he loves them - similar to what Hildago said in another thread, it means he's really, really sleepy.

I despise them. I was in that perfectly dreamy state of almost falling asleep and then one of these violent jerks scares the shit out of me. I can even sense them coming. The dream is always the same. I'm running, running, running through a forest, and suddenly I trip on a root.

Every time I start to dream of running in a forest, my brain thinks, "Uh, oh, here it comes."
posted by peep at 9:04 AM on August 17, 2006

I was once reading an e-book on my Treo 650 (I often "read myself to sleep" in this way) when I nodded off and had one of these grab the tree moments. I chucked the Treo across the room, making quite a racket.
posted by Merdryn at 9:26 AM on August 17, 2006

The falling/tripping/whatever dreams associated with these jerks actually happen after the jerk, but are subjectively experienced as preceding it, at least according to an Oliver Sacks article published in The New Yorker and quoted here.
posted by hilker at 10:47 AM on August 17, 2006

A bit of a derail, but I wonder if this phenomenon is related to the Moro (falling) reflex in babies? Newborns will throw their arms out when jostled a bit during sleep, if, for example, being moved in a carseat. My baby seems to have grown out of it at six months, but I do get the "twitch" quite often, accompanied by the backdated falling dream (tripping over a log while running through the forest, strangely). Monkey brain at work in both cases, I'd guess.
posted by libraryhead at 11:00 AM on August 17, 2006

What's monkeybrains got to do with this?
posted by baylink at 11:07 AM on August 17, 2006

I kept looking, and IMed some anthropologist friends: The hypnic jerk is believed by many to be the Moro Reflex at work in adults. It's thought to be related to our tree-dwelling days as monkeys, where a sleeping startled monkey would thrash out its arms and/or legs hoping to catch a tree limb or vine to prevent itself from falling.

So something startles you awake, and you thrash out, hoping to prevent yourself from falling out of a tree. :)
posted by Merdryn at 11:27 AM on August 17, 2006

Yea! I'm not a freak!
posted by MikeKD at 12:33 PM on August 17, 2006

I think what's happening is that as you fall asleep, your brain shuts off various sensory inputs, including the input from your inner ear. If the brain is still too alert when the input from the inner ear is shut off, this mimics exactly what happens when you fall suddenly: the signal from the otoliths in your semicircular canals is suddenly cut off, and you "thrash out," as Medryn says, in order to catch yourself. This is no more than a minor elaboration of hypothesis #2 in the link Leon provides.

It's interesting how many people in this thread report dreaming of falling. REM sleep typically begins more than an hour into a night's sleep at the end of the first sleep cycle, not when you first fall asleep. Perhaps a Hypnic Jerk at the beginning of the night could be a symptom of sleep deprivation, since that condition will sometimes induce immediate onset of REM sleep.
posted by jamjam at 1:28 PM on August 17, 2006

jamjam - I don't think it's really a "dream" the same way what happens in REM sleep is a dream - it's sometimes referred to as the "hypnogogic phase" - see the second question here.

I recall reading that Richard Feynman used to "imagine" or "dream" of building complex and wonderful Rube Goldberg machines as he was falling asleep. Not really a dream at all.
posted by muddgirl at 4:46 PM on August 17, 2006

I get these frequently... for me the accompanying imagery is either stepping off of a ladder or ledge, or crashing my car. They usually freak out whoever happens to be sleeping next to me at the time.
posted by the_bone at 10:52 PM on August 17, 2006

see also Exploding Head syndrome.
posted by 31d1 at 11:00 PM on August 17, 2006

Response by poster: A derail since a I still have several days before my next allowed official question (but at least it still has to do with sleep and dreams) --

The Olde Wives say one can't die in a dream. Has anybody else actually died in the dream before waking up? {Hmm, I wonder if this hyponogogic reflex is responsible for the tale that you won't hit the ground in a falling dream?} Anyway, in mine, I was stabbed to death... in exquisitely painful extra-super-slo-mo, BTW. Man that dream sensation sucked so bad I still remember it vividly decades later!
posted by CodeBaloo at 12:04 PM on August 18, 2006

CodeBaloo: Yes.
posted by geckoinpdx at 6:16 PM on August 18, 2006

You are right, muddgirl. I was aware of the distinction between dreams and hypnogogic imagery, but I thought the implied duration of some of the reported experiences took them out of the 'imagery' category and made it more likely they were dreams. A look at hllker's link has shown me the error of my ways. Wittgenstein, by the way, argued that all dreams are 'backstories' fabricated by the awakening brain.

AskMeFi is such an amazing place. I followed 31d1's fascinating link about Exploding Head Syndrome and found this collection of personal accounts linked within, and those stories, which I cannot recommend strongly enough to anyone interested in Hypnic Jerks, have changed my view of the subject entirely.

I now think Hypnic Jerks are a mild manifestation, a subclinical manifestation if you will, of Exploding Head Syndrome.
posted by jamjam at 1:10 PM on August 19, 2006

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