I've had these "hypnic jerks" occassionally as long as I can remember and just had one a couple of weeks ago - which is why I clicked on the title of this article.

As far as I can remember (keep in mind I'm half-asleep every time this happens) every single incident coincided with my dream state at the time. In my dream I physically lashed out (e.g. kicked, punched) or fell. I wake up with a corresponding physical jerk of an appendage or my whole body.

I've disturbed the sleep of my bed partner many times when this has happened.

Not just BTW: The animation on this article is fantastic.

@Leonardo: Thanks for the tip. I'll not sign up for any studies on myself!