Fred started to shiver as frantic images of the past flashed through his mind.

frantic 是形容词，由词根 "fren"（表示"疯狂"）和后缀 "-tic"（表示"与...相关的"）组成，意思是"疯狂的、狂乱的"，形容极度焦虑或激动的状态。这里用来描述脑海中闪过的画面是混乱而令人不安的。