out of (one's) skull
Heavily intoxicated by drugs or alcohol, especially to the point of becoming unconscious, nonsensical, or out of control. I think someone might have spiked Jack's drink with some kind of drug, because he's out of his skull all of a sudden.
*out of one's skull
Sl. intoxicated. (*Typically: be ~; go ~.) Oh, man, I drank till I was out of my skull. Two beers and he went out of his skull.