get into one's head
Also, get or take it into one's head. Form an impression, idea, or plan. For example, What strange idea has she got into her head? or He took it into his head that you want to quit. [Late 1600s] Also see get through one's head.
The American Heritage® Idioms Dictionary Copyright © 2002, 2001, 1995 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company.