From Longman Dictionary of Contemporary Englishprey on somebody’s mindprey on somebody’s mind (also play on somebody’s mind)THINK ABOUT if a problem preys on your mind, you cannot stop thinking about it Finally, she broached the subject that had been playing on her mind for days. → mind
Examples from the Corpus
prey on somebody’s mind• Important items which are left have a habit of preying on the mind.• It was Tatiana preying on his mind.• It began to prey on my mind so much that I went to the casualty department of Charing Cross Hospital.• But his main preoccupation was with the unfinished Requiem, which had begun to prey on his mind. 