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lose (one's) marbles
To be or become mentally deficient, incompetent, or deranged; to become of unsound mind. My poor grandmother started losing her marbles after she had a stroke. I've been so sleep deprived lately that it feels like I've lost my marbles!
Farlex Dictionary of Idioms. © 2015 Farlex, Inc, all rights reserved.
lose (all) one's marblesand lose one's mind
Fig. to go crazy; to go out of one's mind. What a silly thing to say! Have you lost your marbles? Look at Sally jumping up and down and screaming. Is she losing all her marbles? I can't seem to remember anything. I think I'm losing my mind.
McGraw-Hill Dictionary of American Idioms and Phrasal Verbs. © 2002 by The McGraw-Hill Companies, Inc.