Go off the deep end

Meaning

To lose control of one's emotions or mental stability. It suggests that someone has abandoned logic or calm behavior in favor of an erratic outburst.

Dramatic, concerned

Used in a sentence

• Ever since he lost his job, he has really gone off the deep end.
• Don't go off the deep end just because the plans changed slightly.
• I think she finally went off the deep end and quit without a backup plan.