go off the rails

Từ điển Oxford Advanced Learner 8th

go off the ˈrails idiom
(informal)
1. to start behaving in a strange or unacceptable manner, for example, drinking a lot or taking drugs
•She went completely off the rails after her sister died.
2. to lose control and stop functioning correctly
•The company has gone badly off the rails in recent years.
Main entry: ↑rail_idiom