Lose Your Marbles

Lose your marbles = lose one's mind, insanity, person who does not have common sense/wits.

"Lose your marbles"
I knew she'd eventually lose her marbles = I knew she'd eventually lose her common sense/rational mind

Have you lost your marbles?. Means the same as "Have you lost your mind"?

By Konstance

Define Lose Your Marbles Meaning