From Longman Dictionary of Contemporary Englishlose your mindlose your mindto become crazy SYN go crazy, go mad Nicholas looked at her as if she’d lost her mind. → lose
Examples from the Corpus
lose your mind• What are you doing on the roof? Have you lost your mind?• Is Roberto correct when he insists that he is innocent and she has lost her mind?• Obviously she was losing her mind.• The musicians are completely losing their minds.• There came a day shortly afterwards when I could no longer ignore the fact that he was losing his mind.• What is not bogus is the position Selda Soyturk is in today because a guy lost his mind behind the wheel.• Some victims feel they are losing their minds or are about to die.• Either she was losing her mind, or she'd followed the wrong man.• PipThe Negro cabin boy who loses his mind when abandoned temporarily in the sea. 