Lose one's head

Mrs. Ambient's grief was frantic; she lost her head and said strange things.

Losing his head entirely, the young collier raved like a madman, what with pain and fear of hospital.

He then had to jump, and appears to have lost his head, as instead of walking the short distance forward to Slochd to let the signalman know what had happened, he started the 6½-mile walk back to Carrbridge.

"He never lost his head in a crisis," Mr. Mandela wrote of his comrade.