Kenneth G. Wilson (1923). The Columbia Guide to Standard American English. 1993.
shook (up) (adj.)
Edited English uniformly uses shaken, meaning upset or disturbed, as the past participle and participial adjective, but Standard speakers increasingly use the Substandard shook and shook up as Casual or Impromptu slang, especially jocularly: I was really shook [up] after the accident.