Pure Pedantry

I get a lot of random questions from friends and relatives. It is an occupational hazard. This one just came down the grapevine:

Do you know how sometimes when you’re lying in bed, starting to fall asleep and all of a sudden it feels like you’re falling?

What does that mean?

What you are talking about is a benign “condition” called a sleep start or a hypnic jerk. I hesitate to use the word condition because these are incredibly common — around 70% of people have these.

What happens is that the whole body jerks one or two times right before sleep onset or during light sleep. This is often accompanied by a feeling of falling or a sensory flash — like lights or a tingling sensation. While they are common in people, they are more common in people with Restless Legs Syndrome (RLS) or people who are sleep-deprived.

The relevant review by Walter (2007) had this to say:

If only one or two whole-body jerks happen occasionally just before sleep onset, consider the diagnosis of sleep starts (also called hypnic jerks). This is common and has been experienced by almost everyone at one time or another. Only on occasion are the hypnic jerks excessive and bothersome to the individual. If the jerks are excessive prior to sleep, the differential diagnosis includes the periodic and aperiodic involuntary movements that are relatively commonly seen in patients with RLS. In a minority of patients with RLS, these movements may be more prominent than the leg discomfort and may be very rapid or myoclonic in speed. In some cases, these very rapid movements in RLS patients during wakefulness electrophysiologically show the characteristics of propriospinal myoclonus, which is initiated by nerve fibers of spinal cord origin. Propriospinal myoclonus during wakefulness in the absence of RLS and PLMS must also be considered in the differential of sleep starts (hypnic jerks), but this appears to be a much less common disorder. According the new International Classification of Sleep Disorders, sleep starts (hypnic jerks) are characterized as follows: the patient complains of sudden brief jerks at sleep onset, mainly affecting the legs or arms; and the jerks are associated with at least one condition from among a subjective feeling of falling, a sensory flash, or a hypnagogic dream. In addition, the disorder must not be better explained by another sleep disorder, medical or neurologic disorder, mental disorder, medication use, or substance use disorder.

Sleep starts are a normal phenomenon occurring in persons of all sexes and all ages with a prevalence of 70%. They presumably arise from sudden descending volleys that originate in the brainstem reticular formation and are activated by the instability of the system at the transition between wake and sleep. Only occasionally do they become excessive, and, in most cases, reassurance that this is a normal phenomenon is all that is needed. There are no known treatments. (Emphasis mine. Citations removed.)

The cause of hypnic jerks is not entirely clear. During sleep onset, a part of the brain called the reticular formation sends a signal down the spine that causes your muscles to relax. (Actually, if I understand correctly, it causes a change in response of motor neurons from activation to inhibition. This is called the “reticular response reversal” and has been the subject of considerable research.) The theory is that occasionally this signal to relax is misinterpreted by the muscles as a signal to contract causing the spasm.

We also know that there is a measurable burst of activity on the EEG during hypnic jerks. This was shown way back in 1959 by Ian Oswald himself. (Oswald is sort of a big-wig in the area of sleep research. OK, fine. Some of you may have heard of him.)

The following is an EEG trace from Oswald’s 1959 paper on the subject (Figure 2):

i-5505cca8b038738a11a3c50f9b1d66da-hypnic.jpg

The arrows indicate the jerk in the leg leads — RL = right leg and LL = left leg. (Yes, I recognize it is hard to see, but it isn’t a very big jerk.) RS is the respiratory trace. The numbers are the EEG leads. ECG is the heart trace.

So the take home message would be that what you are experiencing is totally normal. If it becomes a regular problem, discuss it with your doctor.

—–

Incidentally, any other neurology or neuroscience questions are appreciated and will be answered if they are interesting and if I am not to busy at work that week. You have my email in the Contact section.

Comments

  1. #1 John
    December 13, 2007

    Just had this happen to me the other day. The sensation of falling while falling asleep when sitting on an airplane is even freakier!

    It seems to me that the jerks are more common if i fall asleep while sitting (like in the car or in an airplane) than while laying down.

  2. #2 Carol
    December 13, 2007

    And I’ve always thought I might have epilepsy…

  3. #3 HP
    December 14, 2007

    We used to call this “stepping off a curb.”

  4. #4 Rebecca
    December 14, 2007

    Okay, I understand (more or less) what causes the physical muscle jerk — but I’m still unclear on the cause of the mental sensation of falling. Why falling? Why not…I don’t know…flying? Or eating? Or sex? ;-)

  5. #5 Jake Young
    December 14, 2007

    Honestly Rebecca, they don’t really know. This isn’t an area about which there is a large amount of ongoing research. Further, some people report the falling feeling and some people don’t.

    Sorry. I can’t really tell you.

    If I were to speculate I would say that the reticular system is also linked to your postural reflex system. It signals some of the muscles that make you stand upright. (There is a pathway called the “reticulospinal tract” that does this.) Maybe the signal also is confused as one that suggests that you are falling down?

  6. #6 Rebecca
    December 14, 2007

    Ah…okay! That makes sense to me, too. Thanks!

  7. #7 Interrobang
    December 16, 2007

    Thank you for posting this. I thought it was very interesting and informative.

    It’s interesting that there’s a high cross-correlation between RLS and hypnic jerks (which is a great phrase, by the way). Has anyone done any other research on hypnic jerk frequency in people with disorders that cause involuntary muscle movements? I’m asking because I have the spastic form of cerebral palsy, and I get hypnic jerks a lot, as in I’d say they’re more the norm than the exception. On the other hand, I’d never thought about them too much, because I’ve had them frequently for my whole life and I’ve never seemed to be harmed by them, so I never bothered, say, bringing them up to my doctor or anything.

    I always chalked up the falling sensation to my bad balance and my general fear of falling.

  8. #8 Jake Young
    December 16, 2007

    Interrobang,

    It was my impression reading the literature that hypnic jerks were associated with movement disorders in general, so it wouldn’t surprise me if it was associated with yours. I don’t think that anyone has published a paper about it, but I would bet that it is true.

    Movement disorders are in general associated with a difficulty in motor gating during sleep, and one of the manifestations of that is hypnic jerks, not matter what the disorder.

  9. #9 Macnerdzcare
    December 17, 2007

    i thought this was also a movement disorder.

  10. #10 Owen
    December 17, 2007

    Rebecca: I fence for fun (but not profit), and have sometimes drifted off while thinking about a particular fight or thinking my way through a scenario, and have had hypnic jerks (sometimes involving the whole body) coincide with those sensations.
    Hypnic jerks can also threaten domestic bliss if your partner has fallen asleep and your spasm has woken him/her back up.

  11. #11 bon
    December 19, 2007

    Could this also be caused by taking certain kinds of medications? If so, what kinds?

  12. #12 Jake Young
    December 19, 2007

    Macnerdzcare,

    This is definitely classified under movement disorders, although it is a pretty benign one.

    bon,

    Medications can cause movement disorders or trouble sleeping, but if you read the definition of this disorder it is defined as jerks that are not caused by medications or another illness. This is one of those things that is a diagnosis by exclusion.

  13. #13 Jake Young
    December 19, 2007

    Incidentally, for medications that cause movement disorders during sleep, I think antidepressants, antipsychotics, and stimulants would be the primary offenders. Basically you are looking for any drug that has pro-kinetic side effects to begin with.

  14. #14 gregory
    December 23, 2007

    there is a spiritual explanation for this, it is the moment when awareness stops identifying with the physical mind/body, and falls into the subtle body, on its way to complete disassociation with any of the bodies, what we call deep sleep..

    in the world, many cultures know about these bodies, have for thousands of years… in the backward west though, with our addiction to the religion of science, we think we are discovering things…

    i reckon science wil,l discover the subtle bodies in about fifty years…

    enjoy,… meanwhile, there are other means of knowledge than via the senses and intellect… start meditation… you will see for yourself

  15. #15 Angeline
    December 24, 2007

    When I’m trying to fall asleep when I’m really really tired, I often have a sensation as if I am being rolled over and suffocated by huge cushions or pillows. Sometimes, I also feel as if my body has become extremely bloated and that I am unable to move. This sensation occurs when i close my eyes when I’m about to fall asleep, but dissappears when I open my eyes.

  16. #16 austin
    December 24, 2007

    @ Angelina: I totally know this one, (I think), some kind of size change in my fingers/hands and kinda all over marshmallow-y. Its creepy. I think If i look at the sensory homunculus it happens more in the bigger bits, fingers, hands, lips etc so I just put it down to some sensory accommodation of sleep of some kind.

    For the hypnic jerks, I had heard the explanation was due to the initial stages of sleep paralysis, for a period when you start sleeping I thought your motor functions were kinda disabled (via the RAS), because you don’t want to be motorically ‘living-out’ your dreams. The jerk relates to the brain checking that this is just a motoric state and not a respiratory one too…

  17. #17 Steve
    December 27, 2007

    Does anyone know if there is any research linking nutrition and hypnic jerks? I have been diagnosed with Resless Leg Syndrome and Periodic Limb Movement. While some people only get a few hypnic jerk per night, I get them all night and with great intensity.I eliminated wheat from my diet and it has drastically reduced the intensity and fequency of the hypnic jerks. Although I have not had a recent sleep study to confirm this.(I have had 3 in the past). I can noticably see a difference.

  18. #18 Heike
    June 27, 2008

    how bout neurotransmitter issues like shortage of dopamines or serotonin?

  19. #19 Georgina
    August 12, 2008

    I have these hypnic jerks every time I become drowsy. It is quite alarming to my family if it happens near to them as my whole body shifts off of the surface I am on. There is no sense of falling etc. & it doesn’t always wake me up. However, I often get a fast-beating-heart-sensation following the jerk if it does wake me up & it causes breathlessness as if I’ve run fast. Recently diagnosed with Fibromyalgia after spinal surgery. What is happening to cause this jerk?

  20. #20 Al
    October 18, 2008

    AHH! I can’t believe there are other people who get the marshmellow hand bloating type thing! I have hypnic jerks quite regularly and knew that they were common. Has anyone got anymore information on this subject or can put a name to it? Thanks.

  21. #21 Ethal
    July 17, 2009

    thats funny
    lol
    i was just on a plane today
    and i was half asleep (almost completatly)
    and my legs started to have hypnic jerks
    it was weird to because i sorta opened my eyes
    and my legs were just jumping all over the place
    it also happens to my whole body when im sleeping
    thank for the info
    i was just thinking about it :D

  22. #22 DEBBIE SMITH
    December 15, 2009

    i get this hypnic jerk all the time.although i know its dangerous once it happens i am wide awake again…….i am on anti depressants but even when i haven’t taken my medication for a while it still happens………someone mentioned a kerb.?????…i have that but when you come to step off the kerb,…..there’s nothing to step on to…………sorry guys but really glad it’s not just me…ha ha.sweet dreams.

  23. #23 shannara kelly
    April 3, 2010

    but everytime i sit down i feel like i am falling of a cliff and that once i fell i fall into water with reeds pulling me down andthis has been happerning since my birthday but wen i stand up it stops wat dose this mean.

  24. #24 marc appleyard
    September 30, 2010

    i have the feeling every time i go to sleep i have actaully found my self bounce around the room and go threw walls and hearing a big vibrating noise in my head. it first of all shocked mr so i open my eyes but now i go with it. im not a sleep but i am if that makes sence i hear the tv if my wife is watching it and i can feel i sence of awareness of my surronding me like my wife in bed with me. the only downfall is i awake wth a strong head acke

  25. #25 Cystic Acne
    July 18, 2011

    And do you actually get dizzy and feeling like you are going to pass out? Because my wife just have EEG done because she black out and hit yourself to the skull when she was falling…

  26. #26 alex
    February 14, 2012

    Sometimes i feal i am falling when in my bed and wake up with a shock soon realizing i am just sleeping and fine.

  27. #27 Jude
    February 20, 2012

    I too have thesse ‘falling’ sensations just as I am drifting off to sleep – more commonly when lying on my right hand side (so, I try to settle on the left!!!!!!!). Have also noticed a sense of uncertainty when driving – a sense of dizziness sweeps over my body!!!!! Sounds very dramatic….but feels quite unnerving when behind the wheel!!!!! Any suggestions?????

  28. #28 Savanna
    March 23, 2012

    Well that explains a lot, now I understand I’ve been wondering why this happens since I was little, when I was little I felt like my bed was spinning but now that I’m in my teens its more of the falling feeling, quite amazing how the body works isn’t it? :)

  29. #29 Nikki
    April 12, 2012

    I’m 14 and when I’m about to fall asleep I will have a little vision of my walking my dog, or just going to the park, and suddenly a hole will appear and I will fall in it and wake up, it’s like one of those dreams where you are half asleep and whatever is going on in real life happens in you dream.

  30. #30 David
    April 29, 2012

    I was in bed cuddling partner in the middle of the day and we were both falling asleep. We both woke at exactly the same second because we has both experienced a Hypnic Jerk at the exact same moment. We had both also felt the sensation of falling at the precise same moment as one another. Is this just coincidence or were our bodies somehow feeding off each others energy? Has anyone else experienced this? Thanks