{adj. phr.}, {informal} Acting in a crazy way; especially, wildly crazy. * /The patient was feverish and out of his head and had to be watched./ * /Her friends thought she was out of her mind to marry that man./ Compare: OFF ONE'S ROCKER. Contrast: COME TO ONE'S SENSES.
{adj. phr.} Crazy; mad. * /We had no doubt that the old man was off his head when we saw him jumping into the lake with his winter coat on./