off one's head

prepositional phrase3

1. •
   (UK, informal) Insane, crazy.
2. •
   (UK, informal) Temporarily mentally unstable; very distressed.

   • The kettles they boiled with rage, 'tis said/While ev'ry nail went off its head[…] — 1881
3. •
   (UK, informal) Under the influence of drugs.