Off one's head

The kettles they boiled with rage, 'tis said/While ev'ry nail went off its head[…]

When I had finished I went and saw poor Leo, who was quite off his head, and did not even know me.

Occasionally they seem to go off their heads. Something like epilepsy, you know. It's called Robot's cramp. They'll suddenly sling down everything they're holding, stand still, gnash their teeth—and then they have to go into the stamping-mill. It's evidently some breakdown in the mechanism.

The music is turned up over the conversations, which span global politics, the latest Beyoncé track and anything else randomly entering the minds of us intelligent, but off our heads, savvy young adults.