whiplash

Short definition from Wiktionary

Noun

1. 1
   The lash of a whip.
2. 2
   An injury to the upper spine connected to a violent jerk of the head in either a backward or forward or side to side direction, resembling the motion of a whip.
3. 3
   An abrupt and unexpected change, or the resulting feeling of shock.

Verb

1. 1
   To jerk back and forth; to buffet.
2. 2
   To lash as if with a whip.