Originally posted by JEBOman
I think it could be that your imagination is just getting too tactile (touch oriented), causing you to try and react to it, but since you are sort of asleep and you are not sure how to move, so the signa getts messed up and just kinda jerks you awake
Hmm, very possible. The reason is most likely physical in some way.
There's really no other explanation for the event itself except for hypnagogic imagery. The only logical deduction is just that - hypnagogic imagery sets on.
However, the reason for the jerking...well, as quoted above, seems pretty logical.

Personally, whenever I do remember the thoughts that lead to this they are usually of falling (whether it be falling into an empty space or tripping).