According to Wiki, “a hypnic jerk or hypnagogic jerk, is an involuntary twitch which occurs just as a person is beginning to fall asleep, often causing them to awaken suddenly for a moment.” It is often accompanied with the feeling of falling. When I was younger and such movement would startle me awake, I had the vivid feeling and recollection of tripping while I was walking. The twitch was the moment I stubbed my toe on something and started to go down.
After I started becoming serious about my disc golf game, my mind no longer associated me tripping with the hypnic jerk. Instead I always had the feeling of throwing a drive hard. The jerk was the point in my arm motion where I am most extended backwards and “jerk” to initiate forward arm motion.
Last night I experienced a new visual and feeling associated with the jerk. When my twitch woke me up briefly, I had just done a self set as I was practicing freestyle moves. (A self set is a throw that ideally generates a lot of spin, but almost no forward momentum.) Suffice it to say that freestyle has made its way to my core.