Prey on somebody's mind - Idioms by The Free Dictionary
prey on somebody's mind
prey on (one's) mind
To cause one a lot of worry, concern, or anxiety, especially for a long period of time. I know that money issues have been preying on his mind ever since the company began issuing pay cuts. I really acted like a jerk on Friday night, and it's been preying on my mind all weekend long.
ˌprey on somebody’s ˈmind (also ˌplay on somebody’s ˈmind) worry or trouble somebody very much: The death of his father is really preying on his mind at the moment. He thinks it was his fault. ♢ The question of whether to accept the new job and move to Scotland had been playing on his mind for days.