off the rails

Suggesting the derailment of a locomotive.

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off the rails

1. Used other than figuratively or idiomatically: see off,‎ rail.
2. (idiomatic) In an abnormal manner, especially in a manner that causes damage or malfunctioning
3. (idiomatic) Insane.
4. (idiomatic) Off the intended path.
   • 2009 July 13, Ed Bentley, “Lenin 1, Tsar Nicholas 0 – but Sheremetyevo-3”, in Moscow News:

     ... but the plan came off the rails when infuriated Communists called it "ideological provocation" and warned against "kindling political confrontation

   • 2022 August 10, Mel Holley, “Network News: Question marks over TransPennine upgrade spending”, in RAIL, number 963, page 24:

     "The DfT appears to have put things on a firmer footing, but the path is littered with cautionary tales of transport projects that later went off the rails.

5. (idiomatic) Out of control.
   • 2009 July 10, Jenny Johnston, “You won't catch us going to rehab: So have the young stars of Harry Potter turned into superbrats?”, in Daily Mail:

     I reckon it's pretty astonishing that none of us did go off the rails. There really was no telling how any of us would deal with the pressures and the fame.

• Most commonly used with the verb "to go", but also with forms of "to be", "to come" and others.