Idiom
be out of headbe out of (your) head
British, American & Australian, informal, British & Australian, informal
1.
to be crazy.
He took the car out in this weather - He must be off his head!
2.
(informal, British & Australian, informal) to not be in control of your behaviour because of the effects of alcohol or drugs.
She's completely off her head, she is - what's she been drinking?