shadowcast

sounds like a mix between fear and a myoclonic jerk

I saw apnea's comment and I had no idea what a myoclonic jerk was so here is the definition of the term for those that dont know:
Myclonic Jerk: This term denotes a common experience with sudden contractions of the
big body muscles while falling asleep. This mostly causes a feeling of
stumbling, falling or similar and subsequently waking up again. The
exact cause is not known, it probably is some disturbance in the
brain's functions in the first stage of sleep. Surely it is common,
and does not cause serious problems unless it stops you from sleeping