1. To become insane or mentally unsound; to become extremely foolish or foolhardy. I'm going to lose my mind if I have to hear that song one more time! I think Jane's grandmother has lost her mind lately. You must have lost your mind if you think that's a good idea!

2. To become exasperated, typically due to attempting a difficult undertaking or dealing with a challenging situation. Often used in the continuous tense. I've been losing my mind trying to juggle work, night school, and the kids. Millie was losing her mind trying to prepare food and manage the front of the house, but thankfully she was able to hire someone to help.